Qlttg
Pitbltr library
This Volume is for
REFERENCE USE ONLY
RADIO BROADCAST
VOLUME XIII
MAY, 1928, to OCTOBER, 1928
GARDEN CITY NEW YORK
DOUBLEDAY, DORAN & COMPANY, INC.
1928
. ;•:• : ••-. ••• .-. • ^i-:
* .• *. •• r-:
• • • ••* ••* • »••• •• •
INDEX
(*Illustrated Articles. Editorials in Italics)
PAGE
* A -B-C Power Unit and One-Stage
-tV Amplifier, An Interesting (J.
George Uzmann) 145
*A-Power Unit from Your Battery
Charger, Making an (Robert Burn-
ham) 137
*Adapter for Long- Wave Reception, An
(W. H. Wenstrom) 275
*Adding Regeneration to Any Set (Her-
bert Grove) 210
*A11 About Loud Speakers (Joseph
Morgan) 188
Allocation. The Engineers Plan of . . . 132
*A. C. Receiver, A Dual Control
(Robert Burnham) 192
*A. C. Screen-Grid Receiver, An 37
*A. C. Screen-Grid Tuner, A Two-Tube
(James Millen) 349
*A. C. Super-Heterodyne, A Flexible
(Dana Adams) 39
Amateur Bands, Keep Commercialism
Out of the 254
Amateurs in the Ten-Meter Band 197
'Amplifier and B Supply, A Space-
Charge (H. P. Manly) 163
* Amplifier and Power Supply, A Resist-
ance-Coupled (J. George Uzmann). . 257
*Amplifier Power Unit for the 250, A
Good (Howard Barclay) 141
*Amplifier, The 222 Tube as an R. F.
(Glenn H. Browning) 252
Annual Report of the R. C. A 11
Another Non-Radio Man for the Com-
mission 131
Apparatus, New. . . 35, 85, 139, 227, 284, 372
*As the Broadcaster Sees It (Carl
Dreher) 42, 102, 161, 219, 267, 352
*Audio Combination, The Right (L. W.
Hatry) 23
*Audio Distortion, Checking Up on
(G. F. Lampkin) 290
*Audio Transformer Design, A New
Principle in (Kendall Clough) 133
*Automatic Tuning for the Radio Re-
ceiver (Leroy S. Hubbell) 72
Aviation Must Come to the Use of Radio 129
*Aviation, What Radio Has Done for
(An English Radio Engineer) 288
*O SUPPLY, A D. C. Power Ampu-
le fier and (Victor L. Osgood) 18
*B Supply, A Space-Charge Amplifier
(H. P. Manly) 163
Baird Television Apparatus on Sale, ... 11
*Beat-Frequency Oscillator, How to
Build a (G. F. Lampkin) 156
Book Reviews:
Bible Dramas, by William Ford
Manley (Carl Dreher) 304
Drake's Radio Cyclopedia, by
Harold P. Manly (Carl
Dreher) 302
Elements of Radio-Communica-
tion, The, by O. F. Brown
(Carl Dreher) 306
Experimental Electrical Engi-
neering, by V. Karapetoff
(Carl Dreher) 280
Lefax Radio Handbook (Carl
Dreher) 76
PAGE
Popular Guide to Radio, A, by
B. Francis Dashiell (Carl
Dreher) 76
Practical Radio Telegraphy, by
Arthur R. Nilson and J. L.
Hornung (Carl Dreher). ... 56,
Radio Engineering Principles,
by Henri Lauer and Harry
L. Brown (Carl Dreher) 76
Radio Theory and Operating,
by Mary Texana Loomis
(Edgar H. Felix) 56
What Use Broadcasting? by
William G. Shepherd in
Mirrors of the Year (Carl
Dreher) 274
Wireless Direction Finding and
Directional Reception, by R.
Keen (Carl Dreher) 360
British Imperial Radio System, Struggles
of the 195
British Skeptical of Baird Television Ac-
complishments 69
Broadcast Regulation at, a Standstill .... 130
Broadcast Station Calls with a Past
(William Fenwick) 150
Broadcast Stations, Present Distribution
of. 69
*Broadcasting, How to Improve (John
Wallace) 31
*Broadcasting Is Accomplished, How
Chain (C. E. Dean) 65
Broadcasting, More High Power 69
Broadcasting Needs Capable Leadership. 68
*Building and Operating the A. C. "R.
B. Lab." Receiver (Hugh S. Knowles) 93
*Building the D. C. Lab Receiver
(Keith Henney) 199
/^ALDWELL Hits Straight from the
Ls Shoulder 196
*Can We Multiplex Our Radio Chan-
nels? (Albert F. Murray) 245
*Chain Broadcasting Is Accomplished,
How (C. E. Dean) 65
*Checking Up on Audio Distortion (G.
F. Lampkin) 290
*Coast Survey, Radio Helps in the
(D. L. Parkhurst) 374
Commission Announces Its Short-Watie
Policy, The 196
Commission, Another Non-Radio Man
for the 131
Commission Eliminates Its First Station,
The 132
*Compact and Inexpensive "Trouble
Shooter," A (Emil Reisman) 273
Congress Dabbles with tlie Radio Situation 10
*" Cornet" Multiwave Receiver, The
(W. H. Wenstrom) 77
"Cornet" Receiver, Notes on the
(W.H. Wenstrom) 302
*Coupling Methods for the R. F. Ampli-
fier (Bert Smith) 361
"Crystal Receiver for the Beginner, A
Good (Keith Henney) 97
*T~y C. Lab Receiver, Building the
\-J (Keith Henney) 199
*D. C. Power Amplifier and B Supply,
611307
Bound
PAGE
A (Victor L. Osgood) 18
Direct Selling by Radio (Francis St.
Austell) 58
Directory of Vacuum Tubes, "Radio
Broadcast's" 107, 300
*Distortion, Checking Up on Audio (G.
F. Lampkin) 290
*Dual Control A. C. Receiver, A (Rob-
ert Burnham) 192
TfMPTY Pool, The 255
I-* Engineers in Quantity Production
of Standards 255
Engineers' Plan of Allocation, The 132
"Equalization," The Inequalities of. . . . 131
*Extra R. F. Stage for Any Receiver, An
(The Laboratory Staff) 217
*TTMNE Program You Will Never
" Hear, A (John Wallace) 165
*5-Meter Band? What About the
(Robert S. Kruse) 212
*5-Meter Hints, Practical (Robert S.
Kruse) 371
*5 Meters, Working on (Robert S.
Kruse) 263
*Five-Tube Screen-Grid Receiver, A
(James Millen) 20
*Flexible A. C. Super-Heterodyne, A
(Dana Adams) 39
*From Milliammeter to Multi-Meter
(G. F. Lampkin) . . 80
*f~* OOD Amplifier-Power Unit for the
VJ 250 Tube, A (Howard Barclay . . 141
*Good Crystal Receiver for the Begin-
ner, A (Keith Henney) 97
Guggenheim Fund Shows the Way to
'Frisco 253
TTARRISBURG, III. Needs a 500-watt
Li Station 254
*Haven of a Sea-Going Audion, The
(Raymond Travers) 116
Here and There 12, 70, 197, 255, 339
*"Hi-Q 29," The— A Receiver with a
Band-pass R. F. Amplifier (D. K.
Oram) 341
High-Frequency Spectrum, The
High Power Broadcasting, More 69
*Home Study Sheets, "Radio Broad-
cast's":
Alternating Current 357
Determining the Capacity and
Inductance of a Radio Cir-
cuit 136
Measuring the Amplification
Factor of Tubes 261
Nature of Radio and Electric-
ity, The 135
Ohm's Law 206
Testing Vacuum Tubes 205
Vacuum Tube Characteristics. 262
*How Can Good Radio Programs Be
Created? (John Wallace) 104
*How Chain Broadcasting Is Accom-
plished (C. E. Dean) 65
*How to Build a Beat-Frequency Os-
cillator (G. F. Lampkin) 156
How to Improve Broadcasting (John
Wallace^ 31
FE 26 '29
INDEX— Continued
PAGE
INEQUALITIES of "Equalization,"
J. The 131
"Interesting A-B-C Power Unit and
One-Stage Amplifier, An (J. George
Uzmann) 145
*Is the Highbrow Entitled to a Program
of His Own? (John Wallace) 223
EEP Commercialism Out of the
Amateur Bands 254
K
*T ABORATORY Information Sheets,
-L' "Radio Broadcast's":
A. C. "Universal" Receiver,
The 50
Amplification Constant 112
Audio Transformer, The 380
Calculating Grid Bias for A. C.
Tubes 378
Circuit Diagram, A. C. "Uni-
versal" Receiver 51
Circuit of a Resistance-Cou-
pled Screen-Grid Amplifier. 112
Circuit of the Roberts Four-
Tube A. C. Receiver 298
Circuits of the Hi-Q Six, The. 234
Current 114
Dynamic Loud Speakers, The. 380
Electrical Measuring Instru-
ments 176
Equalizers 232
Equalizing Wire Lines for
Broadcasting 178
Farm Lighting Systems 174
Filters 382
Frequency Characteristic of a
Seven-Mile Cable 232
Grid Bias 50
Grid Bias Circuits for A. C.
Tubes 378
Grid Bias Measurements 50
Hi-Q Six, The 234
Impedance-Coupled Amplifiers 382
Index, August 1927-May 1928 51
Line Voltage Variations 176
Measuring Instruments .... 234, 296
" Motorboating " 110
Power Values in Radio Receiv-
ing Antennas 178
Protecting the Rectifier Tube. 230
Push-Pull Amplifiers 110
Radio Transmission 296
Resistance-Coupled Amplifier
With Screen-Grid Tubes, A 112
Resistors 114
Roberts Four-Tube A. C. Re-
ceiver, The 298
Screen-Grid Resistance-Cou-
pled Amplifier, A 178
Screen-Grid Tube as an R. F.
Amplifier, The 114
Selectivity 230
Servicing Radio Receivers. . . . 294
Size of Tap and Clearance
Drills 298
Soldering Irons 232
Telephone Transmission Unit,
The 380
Text Books on Radio 296
Tube Life 174
Tube Overloading 48
Tuned Circuits 176
UX-250 and cx-350. The 48
Using a Milliammeter as a
Voltmeter 294
Voltmeter, The 382
"Laboratory, "Strays" from the (Keith
Henney) :
A. C. Screen-Grid Tubes 202
A. C. Troubles 83
Another Patent Muddle 260
Another Useful Publication. . . 84
At Last — A Line Voltage
Regulator 259
Coil Dimensions, An Error in . 30
Detector Distortion 29
Engineers as Salesmen 347
"Equamatic" System in Eng-
land, The 29
Finding Ore by Radio ?9
PAGE
Flux for Nichrpme Wire, A. . . 144
From a Lab Circuit Fan 144
High Powered Press Releases. 83
Keeping R. F. Current Out of
the Audio 201
Line Voltage Variations 201
Loud Speaker Tests 202
Loud Speakers 30
Making D. C. Sets Comfort-
able 202
May Standard Frequency Sig-
nals 84
More Radio Hoaxes 259
Mortality Among the A. C.
Tubes 347
New Cyrstal Control 143
Output Transformer Charac-
teristics 83
Present Compression-Type Re-
sistors 144
Present Interesting Trends in
Radio 143
Prices of British "Compo-
nents" 143
Publications Worthy of Note 144
Radio PS a Scapegoat 347
Radio School Scholarships. . . 84
Radio Gossip 143
Real Power from Two 112's . . 29
Recent Articles of Interest ... 202
Recent Interesting Contem-
porary Articles 84
Recent Interesting Technical
Articles 144
Remler A. F. Amplifying Sys-
tem, The 348
Screen-Grid and Automatic
Receivers 259
Screen-Grid Mystery, A 347
Screen-Grid Tube, The: Selec-
tivity 30
Short- Wave Adapter, A 29
Short-Wave Broadcasting. ... 29
Short- Wave Market, The 201
Short-Wave Notes 84
Short- Wave Reception 348
" Sink or Swim " Tube Testing 201
"Skim Milk Masquerades as
Cream " 144
Some Coil Measurements 260
"Strays" from other Labora-
tories. 202
Technical Smoke Screen 144
Tested Products 29
Testing for Soft Tubes 348
Trailing "Power Leak" Inter-
ference 259
Two Interesting Patents 347
Who Our Readers Are 144
Laboratories Grapple with Aircraft Radio,
The 253
Letters from Readers 179, 231, 308, 386
*Lighting Lines Safe for A. C. Tubes,
Make Your (Kasson Howe) 269
List of Short- Wave Stations Throughout
the World, A 44
'Listeners' Point of View, The (John
Wallace) 31. 104. 165, 223
Long Waves Needed in Transoceanic Serv-
ice 255
*Loud Speakers, All About (Joseph
Morgan) 188
Low-Power Stations Plead Their Case,
The 337
X/TACKAY-R. C. A. Struggle, The. . 195
1 VI *Make Your Lighting Lines Safe
for A. C. Tubes (Kasson Howe) .... 269
*Making an A-Power Unit from Your
Battery Charger (Robert Burnham). 137
Manufacturers' Booklets
25, 108, 170, 228, 282, 376
*Manufactured Receivers, "Radio
Broadcast's " Service Data Sheets on
(See Service) 91, 159, 221, 277, 369
"March of Radio, The (E. H. F.)
9. 68, 129, 195, 253, 337
Mergers in the Radio Industry 69
*Milliammeter to Multi-Meter, From
(G. F. Lampkin) 80
249
PAGE
More High Power Broadcasting 69
Monopoly ? Why the Persistent Cry of. . 9
*Month's New Phonograph Records,
The 25, 106
J^TEMA Convention. At the 253
J. V *National Screen-Grid Five, Oper-
ating the (James Millen) 225
Naval Stations. Press, Weather and
Time Signal Transmissions of. . 52
*New Apparatus. .35, 85, 139, 227. 284, 372
*New Principle in Audio Transformer
Design, A (Kendall Clough) 133
*New Transmitting Methods be the
Remedy? Will (Edgar H. Felix) 5
*Newest Power Tube, The (Howard E.
Rhodes) -74
*Nine-Tube Screen-Grid Super, A
(Robert Burnham) 334
No Innovations or Revolutions for 1928 . . 130
*Non-Radiating Short-Wave Tuner, A
fjames Millen) 286
Notes on the "Cornet" Receiver (W. H.
Wenstrom > 302
""pvNE-SPOT" Screen-Grid Super,
\J A (W. H. Hollister)
""Operating the National Screen-Grid
Five (James Millen) 225
*Our Readers Suggest . . .
33, 89, 151, 215, 271, 364
PATENT Situation, The 12
*Phonograph Records. The Month's
New 25, 106
*Photo Broadcasting in England (Wil-
liam J. Brittain) 384
*" Pick-Up" Shall I Buy? What (David
Grimes) 207
Picture Broadcasting Must Contain No
"Ads" 11
Picture Transmission, Regulations for
Teletisinn and 338
*Power Attfiplifier and B Supply, A. D C.
(Victor. L. Osgood) 18
*Power Supply, A Resistance-Coupled
Amplifier and (J. George Uzmann). . 257
*Power Tube, The Newest (Howard E.
Rhodes) 74
*Practical 5-Meter Hints (Robert S.
Kruse) 371
Present Distribution of Broadcast Sta-
tions 69
Press, Weather and Time Signal Trans-
missions of Naval Stations 52
*"O B. LAB." Receiver, Building
iv. and Operating the (Hugh S.
Knowles) 93
*"R. B. Lab." Receiver, A Short-Wave
Adapter for the (Hugh S. Knowles) . . 153
"Radio Broadcast's" Directory of Vac-
uum Tubes 107, 300
*" Radio Broadcast's" Home Study
Sheets (See Home) 135, 205, 261, 357
""Radio Broadcast's" Laboratory In-
formation Sheets (See Laboratory)
48, 110, 174, 230, 294, 378
*" Radio Broadcast's" Service Data
Sheets on Manufactured Receivers
(See Service) 91, 159, 221, 277, 369
*Radio Channels? Can We Multiplex
Our (Albert F. Murray) 245
*R. F. Amplifier, Coupling Methods for
the (Bert E. Smith). 361
*R. F. Amplifier, The 222 Tube as an
(Glenn H. Browning) 252, 359
*R. F. Stage for Any Receiver, An Extra
(The Laboratory Staff) 217
*Radio Helps in the Coast Survey (D.
L. Parkhurst). 374
Radio Laughs at Wired Wireless 10
*Receiver for Short-Wave Broadcast
Reception (Bert E. Smith) 167
Recent Radio Events 132
Regulations for Television and Picture
Transmission 338
"Resistance-Coupled Amplifier and
Power Supply, A (J. George Uzmann) 257
*Right Audio Combination, The (L. W.
Hatry) 23
INDEX— Continued
91
369
221
222
159
160
278
92
370
PAGE
*Roberts Receiver, A Three-Tube A. C.
Operated (Elmer G. Hery) 99
*QARGENT-RAYMENT Seven Re-
O ceiver. The (Howard Barclay) . . . 354
*Screen-Grid Booster for Any Receiver,
A (Glenn H. Browning) 87
*Screen-Grid Receiver, A Five-Tube
(James Millen) 20
*Screen-Grid Receiver, An A. C 37
*Screen-Grid Short-Wave Receiver, A
(Howard Barclay) 203
*Screen-Grid Tube in Popular Circuits,
Using the (Laboratory Staff) 96
*Screen-Grid Tuner, A Two-Tube
(Glenn H. Browning) 27
*S8reen-Grid Tuner, A Two-Tube A. C.
(James Millen) 349
*Service Data Sheets on Manufactured
Receivers, "Radio Broadcast's":
Amrad, A. C. 7, The
Bosch Model 28 Receiver, The
Fada 480-B, The
Federal Ortho-sonic Seven-
Tube Receiver, The
Grebe A. C. Six, The
Kolster 6K A. C., The
Marconiphone Model 61 Re-
ceiver, The
Pfansteihl A. C. 34 and 50. The
Splitdorf "Inherently Elec-
tric " Receiver, The
Stromberg-Carlson Receivers
Nos. 635 and 636 277
"Short- Wave Adapter for the R. B. Lab.
Receiver, A (Hugh S. Knowles). . . . 153
*Short-Wave Broadcast Reception, A
Receiver for (Bert Smith) 167
*Short-Wave Code Signals, A Super-
Heterodyne for (Lloyd T. Goldsmith)
Short- Wave Policy, The Commission An-
nounces Its
*Short-Wave Receiver, A Universal
(Lloyd T. Goldsmith) I...
Short-Wave Stations Throughout ffte
World, A List of
*Short-Wave Transmitter for 1929, A
(Robert S. Kruse) 344
*Short-Wave Tuner, A Non-Radiating
(James Millen)
*Simple Unit for Measuring Impedances
A (F. J. Fox and R. F. Shea)
*Six-Tube Screen-Grid Receiver, A (Mc-
Murdo Silver)
*Space-Charge Amplifier and B Supply,
A (H. P. Manly) 163
""Strays" from the Laboratory (Keith
Henney) (See Laboratory)
29, 83, 143, 201, 261
Struggles of the British Imperial System .
*Super, A Nine-Tube, Screen-Grid
(Robert Burnham)
*Super-Heterodyne, A Flexible (Dana
Adams)
""Super-Heterodyne for Short-Wave
Code Signals, A (Lloyd T. Goldsmith)
15
196
13
44
286
279
281
347
195
334
39
13
'TELEVISION:
A Baird Television Apparatus on
Sale 11
Television and Picture Trans-
mission, Regulations for 338
*Television — Its Progress To-
day (Howard E. Rhodes).. . 331
PAGE
*What Can We See By Radio?
(R. P. Clarkson) 185
*What Hope for Real Televi-
sion? (R. P. Clarkson) 125
Ten-Meter Band. Amateurs in the 197
Tester, A Universal Set and Tube (D.
A. R. Messenger) 148
Three-Tube A. C. Operated Roberts
Receiver. A (Elmer G. Hery) 99
Transmitting Methods be the Remedy?
Will New (Edgar H. Felix) 5
Transoceanic Service, Long Waves Needed
in 255
"Trouble Shooter," A Compact and
Inexpensive (Emil Reisman) 273
Tuning for the Radio Receiver, Auto-
matic (Leroy S. Hubbell) 72
Two-Tube A. C. Screen-Grid Tuner, A
(James Millen) 349
Two-Tube Screen-Grid Tuner, A
(Glenn H. Browning) 27
*222 Tube as an R. F. Amplifier, The
(Glenn H. Browning). 252, 359
*T TNIVERSAL Set and Tube Tester,
U A (D. A. R. Messenger) 148
*Universal Short-Wave Receiver, A
(Lloyd T. Goldsmith) 13
*Using the Screen-Grid Tube in Popular
Circuits (Laboratory Staff) 96
VACUUM Tubes, "Radio Broad-
cast's" Directory of 107, 300
""Vivetone 29" Receiver, The (R. F.
Goodwin) 366
TT/'AR on the Short Waves, The . . 195
FT *What About the 5-Meter Band?
(R. S. Kruse) 212
*What Can We See by Radio? (R. P.
Clarkson) 185
*What Hope for Real Television? (R. P.
Clarkson) 125
*What "Pick-Up" Shall I Buy? (David
Grimes) 207
Why the Persistent Cry of Monopoly ? . . 9
*Will New Transmitting Methods Be
the Remedy? (Edgar H. Felix) 5
*Working on 5 Meters (Robert S. Kruse) 263
AUTHORS
Adams, Dana.
39
Barclay, Howard 141, 203, 354
Brittain, William J 384
Browning, Glenn H 27, 87, 252, 359
Burnham, Robert 137, 192, 334
Clarkson, R. P. . . . 125, 185
Clough, Kendall 133
Dean, C. E. .
Dreher, Carl.
65
. . .42, 56, 76, 102, 161, 219,
267, 274, 280, 302, 352, 360
Felix, Edgar H.
5, 9, 56, 68, 129, 195, 253, 337
Fenwick, William 150
Fox, F. J 279
Goldsmith, Lloyd T . . 13, 15
Goodwin, R. F 366
Grimes, David 207
Grove, Herbert. . 210
PAGE
Hatry, L. W. . . . 23
Henney, Keith 29, 97, 143, 199, 259, 347
Hery, Elmer G 99
Hollister. W. H 249
Howe, Kasson .... 269
Hubbell, Leroy S 72
Knowles, Hugh S. . . .93, 153
Kruse, Robert S 212, 267, 344, 371
Lampkin, G. F 80, 156, 290
Manly, H. P.. . 163
Messenger, D. A. R 148
Millen. James 20, 225, 286, 349
Morgan, Joseph 188
Murray, Albert F 245
Oram, D. K 341
Osgood, Victor L 18
Parkhurst, D. L 374
Reisman, Emil 273
Rhodes, Howard E 74, 331
St. Austell, Francis 58
Shea, R. F 279
Silver, McMurdo 281
Smith, Bert 167, 361
Travers. Raymond 116
Uzmann, J. George 145, 257
Wallace, John .. ..31,104,223
Wenstrom, W. H 77, 275, 302
PORTRAITS
(*Portraits in "The March of Radio")
*Butman, Carl H 69
*Caldwell, O. H. . 69
Conrad, Frank 331
*Duffy, J. P
Evans, Leroy ....
Klemm, Gustav.
*Korn
9
105
.. 166
11
*Lafount, H. A 69
Marconi, G 337
Nakken, Theodor 185
*Pickard, Sam 69
Ray. Bill 166
*Robinson, I. E 69
Stern, Samuel Maurice 105
*Sykes, E. 0 69
Weiner, Michael 105, 223
Zahm, Edna 165
Copyright, 1928, by
DOUBLEDAY, DORAN & COMPANY, INC.
¥
¥
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RADIO BHOADCAST. May. 1928.
Published monthly. Vol. XIII, No
Garden City. N. Y., as second <•
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RADIO BROADCAST
MAY, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XIII. No. 1
»•
Cover Design - - - From a Design by Harvey Hopkins Dunn
Frontispiece - Radio Service in a. Philadelphia Hotel
Will New Transmitting Methods Be the Remedy? Edgar H. Felix
The March of Radio An Editorial Interpretation
Why the Persistent Cry of Monopoly?
Radio Laughs at Wired Wireless
Congress Dabbles With the Radio Situation
Baird Television Apparatus on Sale
Picture Broadcasting Must Contain No "Ads"
Annual Report of the R. C. A.
Here and There
The Patent Situation
A Universal Short- Wave Receiver - Lloyd T. Goldsmith
A Super-Heterodyne for Short- Wave Code Signals
Lloyd T. Goldsmith
A D.C. Power Amplifier and B Supply - Victor L. Osgood
A Five-Tube Screen-Grid Receiver James Millen
The Right Audio Combination - - - - L. W. Hatry
The Month's New Phonograph Records
A Two-tube Screen-Grid Tuner •••_•• Glenn H. Browning
"Strays" from the Laboratory Keith Henney
Detector Distortion
A Short-Wave Adapter
Short-Wave Broadcasting
The "Equamatic" System in England
Finding Ore by Radio
Real Power from two ill's
How to Improve Broadcasting
The Listeners' Point of View
Our Readers Suggest - - -
Remote Volume Control
Improving Your B Device
Plate Detection
New Apparatus
An A.C. Screen-Grid Receiver
A Flexible A.C. Super-heterodyne
As the Broadcaster Sees It - - -
Tested Products
The Screen-Grid Tube: Selectivity
Loud Speakers
An Error in Coil Dimensions
The A. C. "Lab" Receiver
John Wallace
Adjusting Cone Loud Speakers
Selectivity With A. C. Tuhes
Dana, Adams
Design and Operation of Broadcasting Stations:
jy. Frequency Runs
Radio Folk You Should Know: Ho. 5 E. B.
PMibury
A List of Short- Wave Stations Throughout the World
"Radio Broadcast's" Laboratory Information Sheets
No. 185 Tube Overloading
No. 186 The UX-i?o an
No. 187 Grid Bias
No. 188 Grid Bias Measurements
No. 189 The A. C. "Universal" Receiver
No. IQO Circuit Diagram, A. C. "Universal"
Receiver
No. IQI Index, August 1017 — May 1918
No. 191 Index, August 1927 — May 1918
Press, Weather and Time Signal Transmissions of Naval Stations
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Book Reviews
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BECAUSE we value very highly the confidence of our
readers, we present here a few words about the editorial
policy of this magazine as it affects the problem of editorial
ethics. The readers of RADIO BROADCAST are much like the
readers of a magazine devoted to book reviews. In the latter,
editorial articles must deal, perforce, with the same subjects as
found in the advertising pages. In RADIO BROADCAST our
text pages must very often contain articles describing the
use of units featured in the advertising pages. But how long
would you read a book review publication if all reference to
publisher, price and author were omitted? And how long would
you read such a magazine if you felt there were collusion be-
tween editorial and advertising content?
ALL of the articles in this magazine — constructional ones,
especially — are chosen for one reason, only, because we
think they are interesting and useful to our readers. We are
frank about mentioning parts employed because we believe our
readers want to know that information. We have in the past
and will continue to indicate in the future the possibilities of
substitution of parts, leaving the actual construction to the
judgment of the reader. The reader has a right to know just
how any circuit we describe was built, what it costs, and
whose parts are used. In RADIO BROADCAST, all this essential
information is in the article. You will not have to write us for
additional circuit diagrams, a- list of parts or other essential
information which should be in the article in the first place.
Our duty to the reader is to give him articles which are inter-
esting, useful, and complete. If he encounter difficulties, our Tech-
nical Information Service will help him by mail, and the editor
will always be pleased to hear of the results he achieves.
THE technical accuracy of every statement made in this
magazine is carefully checked by Radio Broadcast Labora-
tory, manned by radio engineers all of whom have technical
university training. Their vigilance fortifies every article. Arti-
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of it constructional, some more general, but all with the definite
purpose to be as sound and accurate as we know how. These
requirements invariably apply to all our articles, whatever their
source. Our Laboratory will continue to originate useful cir-
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are constantly sought and will regularly appear. Articles, con-
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when the articles meet our rigid requirements. This is and has
been our practical conception of responsibility to the reader.
THE news of radio developments, no matter where they
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Radio Service in a Philadelphia Hotel
r|^HE Hotel Robert Morris in Philadelphia, in common with
A many other hotels in the United States, has provided its
guests with a compelling reason to stay in their rooms in the
evening The Robert Morris was equipped in March, 1925, and
the unusual feature of the arrangement is that the widest possi-
ble program choice is offered to the listener. A plug with three
jacks is provided in every room and the three jacks provide the
program at the moment being transmitted over the Blue or Red
Networks of the National Broadcasting Company or the Colum-
bia chain. The radio control room is located on the top floor of the
hotel and the equipment, in the main office on the first floor, is
operated by remote control. Constant volume level throughout
the hotel is maintained by using compensating and repeating
coils. By grouping the jacks in the various rooms in parallel series
it is possible to maintain reception in every room in the hotel
even though trouble develop in the outlet in one or more rooms.
WHIPPANY
the Remedy^
By Edgar H. Felix
THE acuteness of the broadcasting con-
gestion problem focusses public attention
upon any method suggested to increase the
capacity of the broadcasting band. Many pro-
posals have been made, some of which hold
promise and others which, if put into practice,
would only increase the existing con-
fusion. Since the regulation of broad- __
casting has become a political matter, "^* —
the great danger exists that the state-
ments of pseudo-scientists may be
accepted and untried plans for station
synchronization will be forced into
practice before they have been fully
developed.
There are only two possible ways of
reducing congestion in the broadcast
band: (i), large numbers of stations
must be eliminated, reduced to part
time, or curtailed in power, or (2), the
number of stations of a given power,
successfully occupying the same chan-
nel, must be increased. Time division
is already practiced to such an extent
that further relief cannot be expected
from this source without too much
restriction of the service and earning
power of existing stations. Power re-
duction will only lessen the value of
better stations; the tendency is toward
increased power because it means
better program service for greater
numbers. Legal and political con-
siderations make it impossible to ex-
pect wholesale station elimination as a source of
the radical improvement necessary for good
broadcasting service in every section of the
country.
Consequently, the only measure of relief
which can be effective is the development of
-n*
Service Range and Interference Range
'"THE following table shows how the power radiated by a broadcasting station
A affects, (a) the "service range," which is that distance over which good recep-
tion will be possible independent of static, day and night, rain or shine; and (b)
the "interference range," which is that distance over which the carrier wave of
a broadcasting station can mar reception by generating a heterodyne whistle
with the carrier wave of another station:
MILES
ANTENNA
SATISFACTORY
HIGH-GRADE
CARRIER
POWER IN WATTS
SERVICE
SERVICE
INTERFERENCE
RANGE
5
10
1
100
50
22.5
3
250
500
65
10
625 .
5000
160
30
1500
50,000
350
90
3000
If we divide the interference range by the high-grade service range we get the
following figures:
ANTENNA
POWER IN WATTS
5
50
500
5000
50,000
INTERFERENCE RANGE DIVIDED
HIGH-GRADE SERVICE RANGE
100
83
62.5
50
33
The figures in the right-hand column show clearly that high-power stations
approach closer to the ideal condition as the ratio of the interference range to the
service range is decreased.
some means of increasing the number of stations
of present powers operating on the same channel
without interference. Many schemes to effect
this result have been offered. They fall into three
classifications:
(i) The elimination of the carrier whistle by
accurate control of the carrier fre-
quency of stations occupying the
same channel, permitting service
range rather than carrier range to
determine the necessary spacing
between stations on the same
channel;
(2) The synchronization of both car-
rier and program, popularly refer-
red to as placing chain stations on
a single channel;
(3) The limitation of the carrier range
to the service range of the station
by the application of new princi-
ples of transmission.
Before considering in detail the
actual methods for each of these
general systems, what are the require-
ments for a plan which will increase
the capacity of the broadcasting band?
Four major qualifications must be met
and failure to meet any one of them
condemns any suggestion as useless.
They are:
(i) The system must be of unfailing
reliability in operation. The adop-
tion of closer spacing among sta-
tions on the same channel, the
objective of most of the systems.
RADIO BROADCAST
MAY, 1928
\
\
\
means that their temporary or per-
manent failure will bring heterodyne
whistles of much greater intensity than
are experienced under present conditions.
(2) The system must not demand an order of
operating skill beyond that obtainable by
average broadcasting station staffs.
(3) The first cost of equipment required and
its maintenance expense must not be so
high as to place it beyond the financial
capacity of average broadcasting sta-
tions.
(4) The adoption of the system must not
require any substantial alteration in
transmitting and receiving equipment
and must entail no sacrifice in quality of
reproduction.
We will examine each proposal in the light of
these four qualifications. The first
general class of methods concerns
those intended to eliminate the car-
rier heterodyne or whistling inter-
ference with which all listeners are
now painfully familiar. The pitch of
the carrier whistle depends upon the ,
difference in frequency between the
twoor more carriers simultaneously
actuating the receiving set. Suppose
we have two stations assigned to a
million cycles, or 300 meters, one
precisely on the assigned frequency;
the other one half of one per cent,
above it, or on 1,005,000 cycles. The
resultant effect will be to impose a
5Ooo-cycle note upon the programs
of both stations. If one station
deviates a hundredth of i per cent,
from the assigned frequency, the
resultant heterodyne will be a hun-
dred cycles. Accuracy of one part in
a hundred thousand is therefore
essential if the carrier heterodyne is
to be reduced to a point below audi-
bility. In that case, the maximum
heterodyne note would be 20 cycles,
assuming that both stations have
deviated in opposite directions from
the assigned frequency. Note the ex-
traordinary stability necessary to
permit two carriers to overlap with-
out heterodyne.
The intensity of the whistle heard
at a receiving point is dependent
upon the carrier energy received
from the more distant station. The
degree to which it mars reception
depends somewhat upon the ratio
of the carrier whistle to the amount
of modulation received from the
nearer station. An understanding of
these two statements will reveal why
carrier synchronization will effec
real relief under present conditions.
You have frequently heard a hetero-
dyne of considerable intensity and waited for the
local station to sign off, in the hope that you
could identify the distant station causing the
whistle. But you find it impossible to hear the
slightest sound from the distant station. This is
due to the fact that the carrier spreads from thirty
to forty times the distance that a high-grade pro-
gram signal is heard and also, because of the
square law operation of the detector tube, the
carrier is subject to much greater amplification
than the audio-frequency modulation impressed
on it
maximum high-grade service range of a joo-watt
station is 30 miles, but its average carrier range
is at least 1000 miles and often over 2000 miles.
Under average conditions, it delivers a dis-
tinguishable program signal to sensitive receivers
for perhaps 350 or 400 miles. If two stations on
the same channel are perfectly synchronized,
they would have to be spaced only 400 to 500
miles apart, without suffering audio-frequency
distortion within their respective local service
ranges. But, under present conditions, ijoo-mile
separation is necessary to reduce carrier hetero-
dyne to the point that local reception is not
noticeably affected and complaints are often
registered with respect to heterodynes caused by
50o-watt stations 2000 miles distant from the
receiving point.
Circle No 1 HIgrKJride Service Range
Circle No. 2 Satisfactory Service Rtnge
Circle No. 3 Interference Range
\
\
i,
i-
\
\
\
SERVICE AREA AND INTERFERENCE RANGE
The circles show the relative areas of high-grade service range, satis-
factory service range, and interference range, of a jo.ooo-watt broad-
casting station. Note how large the interference range is in comparison
to the service range. The actual service area of this station does not
extend beyond the area enclosed by circle No. 2, for at greater distances,
static and fading will interfere with good reception. The much larger
area of circle No. 3 extends far beyond the area of fair reception.
Within this large area the station can create interference by generat-
ing a heterodyne with the carrier wave of another station, supposedly
operating on the same frequency, but actually transmitting on a fre-
quency slightly higher or lower. Accurate stabilization of the carrier
frequencies of stations operating on similar frequencies — perhaps by
the quartz crystal method — will prevent heterodyne interference but
will not prevent interference arising from the clashing of sidebands
Four methods have been suggested for stabiliz-
ing the carriers of broadcasting stations so as to
eliminate the possibility of carrier whistle:
(1) Stable precision crystal oscillators;
(2) Remote manual control of carrier fre-
quency;
(3) Radio transmission of a reference fre-
quency; and
(4) Wire synchronization of carriers.
WHY STATIONS ARE SPACED
IN PRACTICE, this condition accounts for the
great spacing required between stations of
moderate power, if the service area of each of
them is to enjoy undisturbed reception. The
The zero-beat method, employing crystal
control oscillators, is now widely used. The sta-
tion operator wears a headphone through which
courses the output of the crystal oscillator and
also the station's radiated carrier frequency.
The frequency of the station is adjusted until
the two are in exact synchronism so that no
heterodyne whistle is heard.
In preparing to write this article, the author
maintained a broadcasting station on its fre-
quency by the zero-beat method for several
programs. When utilizing a crystal oscillator,
installed at the station, the comparison signal
is constant and powerful. The amount of skill
required and the cost of maintenance of the
equipment needed are within the reach of any
broadcasting station.
Independent crystal control, however, has
been described as too inaccurate and too unstable
to permit the perfect synchronization of two
carriers. As a matter of fact, there is no inherent
fault in the crystal oscillator which cannot be
corrected. What are needed are perfected means
of supplying crystal oscillators with absolutely
constant voltages and means of maintaining the
crystal at an absolutely constant
temperature.
A change of one degree centigrade
varies the frequency of a crystal os-
cillator by sixty to a hundred cycles.
The crystal oscillator is usually in-
stalled in a penthouse on the roof of
a building where the transmitter is
installed. Heat supply is often un-
certain in such exposed locations and
temperature variations of twenty
degrees, during operating hours, are
not uncommon. Such a change is
sufficient to cause a 2Ooo-cycle vari-
ation in the frequency of a crystal
oscillator.
Crystals have been submitted to
laboratories by broadcasting station
owners with a view to finding out
why they do not hold the station to
its assigned frequency. Among these
are ordinary quartz lenses, crudely
scratched and insecurely mounted in
contacting clamps. These worse-
than-useless crystals have been sold
to broadcasting stations with the
expectation that they will stabilize
carrier frequencies. The fact that a
station uses crystal control is no
guarantee whatever that it will re-
main accurately on its frequency
any more than providing an aviator
with a compass assures that he will
arrive safely at a distant destination.
Proponents of the crystal oscilla-
tor method have sometimes proved
their case by setting up two such
oscillators in the laboratory, both
using a slab from the same quartz
crystal. Such demonstrations, how-
ever, prove nothing because both
oscillators are then working under
exactly the same conditions. When
one of the oscillators is shipped to a
distant station to control its carrier,
varying temperature conditions
cause sufficient deviation to produce annoying
heterodynes. With equipment now commercially
available, the crystal oscillator does not possess
sufficient stability to eliminate the heterodyne
whistle between two stations operating on the
same channel. Nevertheless, development of
precision oscillators, with accurate temperature
control, is a most promising line of research.
MANUAL CONTROL OF FREQUENCY
A NUMBER of enthusiasts have loudly
heralded their success in synchronizing
their station's carrier with a single interfering
station by checking the heterodyne with a receiv-
ing set remote from the broadcasting station.
This is the second method listed. By means of a
wire connection with the station, the carrier
frequency is varied until the observed heterodyne
MAY, i9a8
WILL NEW TRANSMITTING METHODS BE THE REMEDY?
disappears. Because, in isolated instances, two
stations have employed this method successfully,
it has been hailed as a panacea. In those cases
where two stations, assigned to the same channel,
cause a heterodyne sufficiently loud to permit
of easy elimination by the zero-beat method,
they both suffer audio-frequency distortion, due
to the interaction of their programs, even
within their immediate service areas.
Although the heterodyne whistle may be
eliminated, the system does not permit of ac-
curate synchronization unless the receivers used
respond to frequencies below sixty cycles. Fur-
thermore, the scheme merely accomplishes ap-
proximate synchronization between two stations
and affords no assurance that either station is on
its assigned frequency. Should any number of
stations on the same channel use this plan, that
frequency would become a raving bedlam, each
station trying to follow the others, each not
knowing what changes to expect in the frequency
of the others. The difficulties of manual fre-
quen<-y control can best be appreciated by set-
ting up three or four regenerative receivers in
neighboring houses, adjusting them all in an
oscillating condition upon a predetermined
broadcasting station, and maintaining them
there without permitting an audible whistle.
The third plan listed is theoretically most at-
tractive. A short-wave station is to radiate a
national synchronizing signal, to be used as a
reference frequency by all broadcasting stations.
This is accomplished by radiating a io,ooo-cycle
note, impressed by modulation on a short-wave
carrier. A receiving set, installed at each broad-
casting station, would pick up this signal, supply
it to a harmonic producer which multiplies the
received note to the assigned frequency of the
station. The station's carrier would then be
adjusted until it zero-beat with the output fre-
quency of the harmonic producer. The transmit-
ted synchronizing signal cannot be higher than
10,000 cycles because it must be a multiple of
every frequency used as a broadcast carrier.
The manual control of a broadcasting station's
frequency is difficult enough when a local crystal
oscillator at the station itself furnishes the ref-
erence frequency. But to use for this purpose a
weak and varying national synchronizing signal,
transmitted in most cases more than a third of
the way across the country, is like trying to
balance an egg on your nose. The carrier fre-
quency of a broadcasting station is constantly
subject to slight variations, due to changing
temperatures of vacuum tubes, voltage changes
in the main power supply, and the effect of modu-
lation peaks. Each of these variations must be
compensated by readjustment of the carrier
frequency. The source of the reference or com-
parison frequency must therefore be perfectly
stable.
A NATIONAL SYNCHRONIZING SIGNAL?
THE principal difficulty with the national
synchronizing signal plan is that the entire
country cannot be successfully blanketed by the
output of a single short-wave station at all hours
of the day and night. The received signal must
be sufficiently strong and stable to actuate
a harmonic producer and produce a steady ref-
erence frequency for every broadcasting station
in the United States. The system does not meet
the requirement of reliability. The cost of main-
taining a national synchronizing station in con-
tinuous operation, even if divided among 700
broadcasters, and the rather elaborate receiving
equipment needed at each station is a serious,
though by no means insurmountable, barrier to
ihe plan.
1 he fourth method is the employment of wire
lines for synchronizing s' itions. In the case of
Energy from Station
Nol
Energy from Station
No 2
Resultant Energy
Intercepted by
Receiving Sets
r
Resultant Audible
Heterodyne Whistle
in the output ofthe
Receiver
WHEN TWO STATIONS INTERFERE
Station I may be operating on its correct fre-
quency, but Station 2, which we will assume
should be on the same frequency, may be slightly
off its assigned frequency. A receiver tuned to
Station I also receives energy from Station 2.
The third curve shows what happens in the
detector circuit: the two waves combine and in
the loud speaker there is a heterodyne whistle,
constant in pitch, indicated by the fourth curve.
If the whistle is loud enough, it will completely
ruin reception. Accurate stabilization of the
carrier frequencies of all broadcasting stations
within an accuracy of at least .05 per cent, is
absolutely essential if reception is to be free of
heterodyne interference due to this cause
chain broadcasters, it might be possible to use the
order wire circuit interconnecting chains, but,
since chain circuits are set up for only an hour or
two each evening, the contribution to stability
which this would afford is quite negligible. There
are not enough telephone wire facilities to spread
a national synchronizing signal to every city
where a station exists. The cost of interconnect-
ing hundreds of stations would run into several
million dollars annually. The economic burden
which wire synchronization on a national scale
would impose is entirely beyond the capacity of
the broadcasting industry to bear.
LOCATION
OUTSIDE
OF CITY
LOCATION
IN CITY
18 Per Cent.
1 69 Per Cent.
1 3 Per Cent.
28 Per Cent.
45 Per Cent.
27 Per Cent.
Fair Service
Good Service
Very Good Service
STATIONS SHOULD BE OUTSIDE CITIES
The drawings show the relative effectiveness of
two transmitters of equal power, one located in a
city and the other outside. As many listeners as
possible should be included within the good
service area of a station, which is possible by
locating the station outside of a city. Under such
conditions, 60, per cent, are located in the area of
good service compared with 45 per cent, in the
previous city location. Locating a station outside
of a city distributes more evenly the field
strength of the signals because the absorption
effect of steel buildings is removed. (Data from
Hell System Technical Journal, Jan. 1927)
With respect to the second problem, the syn-
chronization of both program and carriers on the
part of chain stations, many of the considerations
already discussed apply. The outstanding ex-
ample of carrier and program synchronization
has been the successful simultaneous operation
of WBZ in Springfield, Massachusetts, and WBZA
in Boston. A special channel is utilized to trans-
mit a synchronizing signal so that both stations
take their carrier frequency from the same
frequency source. Both stations invariably
broadcast the same program. The results of this
experiment have been satisfactory and the
question is often asked why all the stations of the
Red Network, for instance, do not synchronize
their carrier frequencies in the same way so that,
instead of occupying ten or twelve channels,
they would use but one.
The task of carrier and program synchroniza-
tion of WEAF and WLW, for example, as compared
with the synchronization of WBZ and WBZA,
presents some curious problems, the importance
of which is not generally realized. In the first
place, WBZ and WBZA are separated by only
seventy miles, while WEAF and WLW are 570
miles apart. This eight-folds the wire leasing
costs for synchronizing the latter two stations,
making a truly imposing financial burden.
Secondly, the two stations do not continuously
and invariably radiate the same program. Were
they to radiate two different programs, audio-
frequency distortion of both programs would be
sufficient to cripple the entertainment value of
both stations, even well within their local service
areas. Third, since large areas receive signals
from both WEAF and WLW in appreciable
amounts, the received signals in such areas would
cause phase distortion. The reason that phase
distortion is not experienced more generally in
the WBZ-WBZA combination is that, because of an
inexplicable ether wall, there are few points
where an appreciable signal is received from both
stations.
Considering that radio waves travel 186,000
miles a second, it is hard to conceive appreciable
lag in the reception of the same program radiated
simultaneously from two different stations at
varying distances from a receiving point. But,
even in the hypothetical case of WEAF and WLW
this lag may cause serious distortion. A listener
at Staunton, Virginia, where both WEAF and
WLW are received with good volume, is approxi-
mately 272 miles from Cincinnati and 365 miles
from Bellmore. The distance from Bellmore is
93 miles greater than the distance from Cin-
cinnati and therefore, theoretically at least, the
program from Bellmore would lag BJff of a^
second behind that from Cincinnati. This would
cause serious distortion. Some frequencies in
the musical scale would be exaggerated and
others reduced in intensity.
Experience with the reception of several
signals from the same station, through the effect
of reflection and the influence of bodies of water
resulting in phase differences, offers valuable
evidence, tending to confirm the distorting
effect of synchronized chain broadcasting where
the receiver responds appreciably to signals from
more than one broadcasting station.
Ordinarily, the reception of two or three
signals from the same station does not seriously
affect quality because one of the signal sources
usually predominates over the others sufficiently
to make their influence negligible. But there are
many known cases where phase distortion ac-
counts for the poor quality with which high-
grade stations are heard in some areas. \\ hen
WEAF broadcast from Walker Street, several
years ago, listeners in Pelham, New York, but
16 miles airline distance from the transmitter,
complained that, even with the best Of recei\ers.
8
RADIO BROADCAST
MAY, 1928
only a weak and distorted signal could be re-
ceived. A thorough investigation with loop re-
ceivers and field strength measuring equipment
revealed that two signals from WEAF, apparently
coming in from two different directions and, at
some points, exactly 180 degrees out of phase,
tended to cancel each other. Similar effects would
be experienced when two stations radiate identi-
cal programs on the same channel.
If a chain'of twenty stations were synchron-
ized, the resultant reception, at all points beyond
the high-grade service range of the synchronizing
stations, would at least lack that clearness and
purity of tone which characterizes modern broad-
casting and might be sufficiently confused to be
almost unrecognizable. Because of this con-
sideration, desirable synchronization of chain
programs is limited to stations widely separated
geographically so that no listener is within the
practical range of more than one synchronized
station.
CHAIN STATION SYNCHRONISM
THE practical application of synchronization
of chains is thereby limited to the establish-
ment of two or three groupings per chain rather
than placing all the members of a chain on a
single channel. This would not effect radical
saving of cleared channels, a maximum of four
or five for each chain being possible.
A further barrier to extended chain synchroni-
zation is the fact that it can conserve channels
only if the stations involved broadcast chain
programs exclusively. Since most of the subscrib-
ing stations use chain programs only occasion-
ally, an hour or two each evening at the most,
permanent assignments to synchronized channels
is now impossible. The cost of wire lines and
chain features is altogether too high to require
subscribers to chain programs to utilize only
chain programs. Yet, only under those condi-
tions, would chain synchronization effect any
economy of channels. Most chain stations broad-
cast local programs and perform local services
during a majority of their broadcasting time.
These services would have to be discontinued or
transferred to minor stations under any plan of
widespread chain program synchronization.
Considering that the problem is to find com-
fortable room for nearly 700 stations in a band
of 89 channels, reliance upon the single measure
of chain station synchronization does not offer
any promise of real relief, even if the difficulties
cited could be overcome immediately.
A trend of development which holds some
promise is improvement in the permissible per-
centage of modulation without resultant distor-
tion. This is the third general measure of relief
given at the beginning of this article. Its effect
is to increase the percentage of the high-grade
service area to the total carrier interference range
area. The experimental fifty- kilowatt transmitter
at Whippany. maintained by the Bell Labora-
tories, utilizes a new method of combining carrier
with program signal, said to effect one hundred
per cent, modulation. While the results, so far as
increased service range for a given carrier power
is concerned, are not startling, they are, never-
theless, appreciable. The engineering ideal to
be attained in this direction is that the carrier
shall cease to radiate at the edge of the station's
high-grade service area. The problem of setting
up an intense wave motion of any kind and mak-
ing it cease abruptly at the limit of its usefulness
is a tremendous challenge to engineering in-
genuity. In radio transmission, there is room for
so much improvement in reducing the ratio of
carrier spread to useful service range that some
progress in this direction may be hoped for.
But that this development will have material
bearing in the present situation is not within
the expectation of the most sanguine workers in
this field of research.
Considering the immediate possibilities of all
the proposed measures of relief, none holds
greater promise than the development of high-
precision crystal oscillators with accurate tem-
perature control. Realizing the value of a source
of constant-frequency oscillation, many labora-
tories have been concentrating on this problem
during the last few months. The writer has seen,
in the development stage, a new type of quartz
crystal precision oscillator for broadcasting sta-
tions which will probably be marketed by the
R. C. A. This device will consist of two ac-
curately ground and matched quartz crystals
mounted in a constant temperature chamber.
The temperature is kept constant by means of a
thermostat and maintained at a given setting
WIDTH OF CHANNEL WIDTH OF CHANNEL
CARRIER PLUS SIDE BANDS CARRIER PLUS SIDE BANDS
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"CARRIERS" AND "SIDEBANDS"
Stations assigned to adjacent broadcasting chan-
nels transmit on carrier frequencies differing by
10,000 cycles. When programs are transmitted,
two sidebands are produced which introduce
into the transmitted wave, frequencies up to
5000 cycles above and 5000 cycles below the
carrier frequency; the station therefore uses a
band of frequencies 10,000 cycles wide. The
left sketch shows the frequency bands used by
two adjoining stations. The two carrier fre-
quencies differ by 10,000 cycles; the sidebands
meet each other but do not overlap. This holds
true when two adjacent stations hold exactly
to their assigned frequency. If either station
varies, the condition shown at the right obtains,
where we have assumed that one station has
wandered from its frequency to the extent of
4000 cycles (4 kc.) deviation. This leaves the
carrier separation between the two only 6000
cycles (6 kc.). Then, in the receiver output, we
would hear a 6ooo-cycle note, which may be
loud enough to ruin reception. Interaction be-
tween the two sidebands of the stations — shown
on the shaded portion of the diagram — also
occurs
by means of this thermostat, checked by a
thermometer. A suitable heating coil is also
mounted in the constant temperature chamber.
The two crystals, supplied with this oscillator,
may be ground to any one frequency in the
band of from 550 to 1500 kilocycles. A small
selector switch is arranged to select either of the
two crystals. Should one of the crystals fail dur-
ing the operation of a broadcasting station, it is
only necessary to throw this selector switch
which removes the defective crystal and cuts in
the spare crystal, which will be at the right
temperature to start operation immediately.
The oscillator circuit will consist of a vacuum
tube and coil system, the electrical constants of
which have been very carefully determined with
a view to being suitable to work with the quartz
crystals. A monitoring receiver, comprising a
suitable detector and two stages of audio-
frequency amplification, in a separate box, has
also been designed for use in connection with the
quartz crystal precision oscillator. When these
two boxes (the quartz crystal oscillator and the
monitoring receiver) are used in conjunction, a
loud speaker may be connected to the output of
the last stage of audio-frequency amplification
and the quartz crystal frequency beat against the
carrier of the broadcasting station. Special
precautions will be taken to emphasize the low
frequencies so that the zero-beat note will be
heard at its greatest efficiency.
No definite claims have yet been made as to
the stability of this device, but there is no ques-
tion that two stations, operating on the same
channel, both employing the device, will not
heterodyne each other seriously. It should elimi-
nate the high pitched squeal and that, alone, will
justify its installation. It is not unreasonable
to expect that, with continued improvement
and experience with precision quartz crystal
oscillators, complete carrier synchronization
will ultimately be made possible.
NEW METHODS OF TRANSMISSION
THIS summary would be incomplete if
mention were not made of several proposed
new methods of transmission, claimed to reduce
the width of the channel required by a broad-
casting station. These methods are frequently
mentioned in public statements, issued as possi-
ble measures of relief by persons who must know
the objections to their adoption in the broad-
cast band. One is single side-band transmission,
accomplished by suppression of the carrier and
one side-band, as utilized in practice in the
transatlantic telephone. It has the vital objec-
tion that its adoption is predicated upon scrap-
ping every transmitting and receiving equip-
ment in the country. The broadcast receiver
necessary to pick up single side-band trans-
mission is expensive and delicate. One of its
elements is an oscillator which must be adjusted
to within ten or fifteen cycles of the assigned
frequency of the station to be received, in order
to supply the missing suppressed carrier. To
reequip every broadcast listener with a suitable
receiver under this system would cost the public
not less than half a billion dollars.
Another suggestion along these lines is the
adoption of a new system of frequency modula-
tion. For this has been claimed the extraordinary
virtue of accommodating simultaneously be-
tween one and two thousand broadcasting sta-
tions in the present band. The basic principle of
the system is that the carrier frequency is shifted
up and down according to the desired audio
signal to be transmitted. The receiving set is
tuned with extreme sharpness so that the shifting
carrier causes varying energy to actuate the
receiving set by reason of the detuning effect.
This sytem would also require the scrapping of
all receiving sets, unless the carrier is shifted
over so wide a scale that no economy of channels
is effected. The contention is also raised that a
shifting carrier sets up numerous, harmonics so
that the theoretically narrow band occupied
by the frequency modulated carrier would prove
to be in practice no narrower than that used by
broadcasting .stations operating under the
present simple methods of modulation.
A most exhaustive study of the entire subject
will lead inevitably to the conclusion that prog-
ress in increasing the capacity of the broadcast-
ing band will be steady but that no radical
developments, sufficient to offer a complete
solution to the present problem, are in sight.
IME.W.S' AND INimPUnATION OK r.iiUWNT UAhlQ EVHM'I'.S
Why the Persistent Cry of Monoply?
THE struggle now shaking the foundations
of the radio industry has long been brew-
ing. On one hand is assembled a group of
militant independent manufacturers, vigorously
attacking an alleged monopoly whose grasping
tentacles reach into every branch of the radio
field; on the other hand, the radio mouthpiece
of vast electrical interests, claiming, with injured
innocence, that it was born out of patriotic mo-
tives and possesses its imperalistic power over
the radio industry by virtue of its widespread and
proper patent rights. Drawn into this conflict are
the Federal Courts, the Federal Trade Com-
mission, Congress, and the Federal Radio
Commission.
The consequences of this struggle may be far-
reaching. So great is the patent strength of the
combination that little reliance is placed upon
upsetting the validity of enough patents which it
holds to free the industry of its domination. Nor
is there any vast sum being spent in research to
develop non-infringing vacuum tubes and as-
sociated circuits. Instead, attack has been made
upon the methods used in taking advantage of
its patent position and upon the fundamentals
of the patent itself.
Several bills before Congress propose drastic
revision in the powers conferred upon all patent
holders; one, for example, seeks to make revoca-
tion of patents the penalty for violation of anti-
trust laws so that companies conducting research
and promoting progress will suffer more severely
than those which simply copy designs and in-
fringe patents. Another bill proposes that pat-
ents applying to vacuum tubes shall not confer
upon their holders the same rights which apply
to all other articles, a plain discrimination against
one industry.
Another line of attack is through the Federal
Radio Commission. The commission is severely
criticized by Congress, to which it reports, and
by hostile station owners, for the privileges ex-
tended to the chain stations, partly owned by
the combination. Bills proposing equal geo-
graphic distribution of broadcast transmitters
are being written, requiring the destruction or
curtailment of useful and popular broadcasting
services. The operation of such a law would in-
evitably require power reductions on the part of
WEAF, wjz, WGY, and KDKA, all N. B. C. stations.
No avenue is being overlooked to injure, directly
or indirectly, any and every activity of the com-
bination.
Let us view the situation sanely. A wave of
resentment has arisen against the power of the
Radio Corporation of America and the huge
electrical interests backing it. This power is
based upon the ownership of patents, in them-
selves a legal monopoly. The restrictions imposed
by patent holders are escaped either by abandon-
ing the field, paying royalties, or devising new
methods which do not infringe. Many companies
in the radio industry have elected to pay royal-
ties. There is no indication that any of the un-
licensed independents are making any real effort
to devise non-infringing designs. They elect to
follow none of the three customary alternatives.
Politics have further clouded matters in a fog
of flaming oratory. Bills are proposed, with the
intention of injuring the Radio Corporation of
America, which, if passed, will accomplish that
objective, but will also mutilate both the present
broadcasting structure and the entire patent
structure upon which American industry has
been built. The. Radio Corporation of America
should be punished for any crimes of which it is
guilty, but it would be unfortunate if unwise
legislation were enacted in the current anxiety
to inflict punishment.
The foundations for the present situation were
laid shortly after the war. American communica-
tions had been greatly hampered, both during
and after the period of neutrality, by foreign
censorship and foreign ownership of cables and
long-distance radio communications. Naval
officials desired the establishment of an American
owned transoceanic network and an American
radio industry so that channels of communica-
tion and sources of supply for war needs would
always be available. No one company had access
to a sufficient number of patents to enable it to
conduct a profitable transoceanic radio service
or even to manufacture modern vacuum-tube
transmitting and receiving apparatus.
With the encouragement of high naval officials,
the Radio Corporation of America was formed
in 1919. It was given rights, in a patent pool
comprising the principal radio patent holders,
to conduct transoceanic services and marine
communication and also to sell transmitting and
receiving apparatus to the handful of amateurs
then operating. The pool consisted of the Amer-
ican Telephone & Telegraph Company and its
subsidiary, the Western Electric Company, the
General Electric Company, the Westinghouse
RADIOMARINE CORPORATION ORGANIZED
The ship-to-shore marine radio communications
of the Radio Corporation of America were trans-
ferred to a new subsidiary, the Radiomarine
Corporation with which was combined the In-
dependent Wireless Company. Charles J.
Pannill, former president of the Independent, is
now vice-president and general manager of
Radiomarine and J. P. Duffy, for years superin-
tendent of the New York division of RCA
marine, has been appointed superintendent of
operations. Mr. Duffy is shown above
Electric & Manufacturing Company, and the
Wireless Specialty Apparatus Company. Each
company threw their radio patents into the
pool and received license under all the patents,
each for use in a particular and limited field of
activity. The fundamental objective of the com-
bination sought by the Navy was promptly
accomplished. The world-wide communication
system came into being. Had this been the
only result of this pooling arrangement, there
would be no conflict to-day.
Radio broadcasting came in an avalanche of
public enthusiasm in 1920 and 1921. It is obvious
to anyone who has read the original agreement,
upon which the patent pool is based, that broad-
casting was not contemplated when the pool
was formed. But the patent structure which was
thus built up has established an almost impreg-
nable domination of the radio industry. Con-
sidering the immense research facilities of the
group and the important patents which its vari-
ous members have purchased, it is in a position
to maintain that hold, unless its patent rights
are abridged or modified.
At the beginning of the radio boom seven
years ago, few of the group's radio patents had
been adjudicated. An independent industry grew
up and flourished in total disregard of these
patents. A few gestures were made by the group
to make known its patent holdings, such as send-
ing infringement warnings to manufacturers by
registered mail regarding the Pickard crystal
patents, but no effort was made to make the
public conscious of the importance of the poo],
its research facilities, and the patents which it
held. Suits were filed which are only now being
finally settled.
With recent adjudications, all of the large
producers, representing about three fourths of
the industry's volume, have become licensees of
the group. The remainder have been unable or
unwilling to meet the license terms, with their
minimum annual royalty guarantee of $100,000.
The independent vacuum-tube industry has
been virtually destroyed by the effects of one of
the clauses of the license contract which requires
that all licensed radio sets be equipped with tubes
sold by the R.C. A. or Cunningham, a subsidiary.
This clause has been adjudged as a case of re-
straint of trade under the Clayton Act. The
R. C. A.'s justification might be among other
things, that no one can make tubes without
infringing their patents (adjudicated and un-
adjudicated), and hence there is no legal com-
petition.
This, briefly, and stripped of many ramifica-
tions, is the background of the situation. The
combination was formed with a useful and pa-
triotic purpose which has been successfully ac-
complished. Its existence was also instrumental
in initiating the first permanent broadcasting
and, more recently, in making possible a source
of a comprehensive license to manufacture radio
receiving sets without infringement of any but
a few patents held outside of the group. Several
members of the combination are responsible for
vitally important research work, contributing to
the modern standard of radio reproduction.
Strongcompanies anddominent groupsexist in
10
RADIO BROADCAST
MAY, 1928
every important field of industry. But in none is
the dominant group so generally disliked and so
freely criticized. Mention of the General Motors
to an independent automotive engineer or motor
car wholesaler does not have the effect of ruining
his digestion or moving him to profanity. Why
all this resentment against the radio combina-
tion?
The Radio Corporation of America is singu-
larly devoid of public relations sense. 1 1 has never
effectively set itself to the task of winning public
goodwill. Only when under attack does it offer
belated explanations. It conducts its affairs in a
dictatorial manner, deciding for itself what is
good for it and what is good for the entire in-
dustry. It regards the interests, but apparently
not the opinion, of the public. The severest pen-
alties are imposed by the court of public opinion.
We must distinguish between publicity and
public relations. Publicity is a matter of releas-
ing information to the press. In this respect the
R. C. A. is highly efficient. It issues publicity
material copiously. Public relations involve
every relationship with those outside a company's
personnel, not merely relations with the press.
The building up of satisfactory public relations
requires that every act, however small, be con-
sidered in the light of public understanding and
interpretation.
It may be legal to collect royalties based on
the gross business of a licensee, but how will the
public react to the knowledge that one manu-
facturer, making a cheap table model radio set,
pays three or four dollars royalty on each set he
makes, while another, using the same patents in
the same way, pays fifteen or twenty dollars
because his set is of high quality and is housed
in a piece of fine furniture? How will the public
feel when it learns that R. C. A. patent royalties
have been sufficiently large to add greatly to the
cost of producing radio sets and to make the
operations of some of the most successful inde-
pendent companies almost profitless?
An early adjustment of the present situation
must be effected, lest it cause the passage of
legislation detrimental to all patent holders. Any
law which makes a patent less valuable and offers
less protection to the owner of a patent will
discourage scientific research and rob the inde-
pendent inventor of his incentive to devote him-
self to progress. Unless considerable forbearance
and cool judgment is displayed by all the parties
involved in the present controversy, the only
possible outcome is legislation which will per-
manently weaken our patent structure. Aroused
public opinion may exact too great a penalty,
unless the patent holding group be guided by
more of the spirit of live and let live.
Radio Laughs at Wired Wireless
OUR contemporary, Radio Retailing, leads
off, in a recent issue, with a stirring edi-
torial to the effect that the radio industry
can no longer "laugh off" the approach of wired
wireless. It states that the program services,
which the electric companies will soon pour into
American homes via the power lines, will be
superior in quality to "space" broadcasting and
hints that radio will have difficulty in competing
with them. The publication solemnly warns the
radio industry to prepare for the competition
of wired wireless.
Because of the well-earned reputation of our
contemporary, these editorial remarks have
created some uneasiness in the radio trade. It is
our view, however, that we can "laugh off"
wired wireless competition for many a year. In
fact, we very gravely doubt that the future of
wired wireless is as rosy as Radio Retailing be-
lieves it to be.
If the electric power companies can find better
symphony orchestras than the Philharmonic
and the New York Symphony, more important
prizefights than the Dempsey-Tunney, better
bands than the Marine Band and the Goldman,
greater artists than Jeritza, Mary Garden, Galli
Curci, John McCormack, Gigli — oh well, what's
the use of continuing — anything they can un-
earthwill quickly be recruited to the broadcasting
field. The power companies will require as
elaborate and as expensive transmission equip-
ment as do broadcasting stations serving an equal
area. There is no reason to believe that the wired
wireless company can secure talent at a lower
cost than can broadcasting companies. They
A SAMPLE OF FACSIMILE TRANSMISSION BY THE KORN SYSTF.M
cannot claim better transmission quality because
power lines also have their share of atmospheric
noises and, in addition, current surges and dis-
turbances which are fully as great, if not greater,
than those with which radio contends. They
cannot claim more faithful reproduction because
radio now encompasses practically all the fre-
quencies heard by the human ear. Wired wireless
has no advantage over radio in cost of program
and technical operations or in reproduced result.
The most important claim, made by the sup-
porters of wired wireless, is that it will not put
forth publicity programs. Wire broadcasting will
derive its revenue, not from transmission, but
from reception. The consumer will pay directly
at a rate probably ranging between three and ten
or twelve dollars a month, depending upon
whether he is content to use headphones or
wishes high-grade loud speaker reception. We
hazard the prediction that the electric power
companies will, sooner or later (and probably
sooner), yield to the temptation of making oc-
casional remarks about electrical appliances,
good lighting and a few other things which will
promote the sale of electrical apparatus and in-
crease current consumption. The monthly wire
broadcasting toll will be a much more serious
obstacle to spreading wired wireless than is the
publicity accompanying commercial radio pro-
grams to the growthof the broadcasting audience.
I he American public is not accustomed to
paying for something which it can secure without
direct payment. The monthly payment feature
of wired wireless will confine its market very
largely to public places, such as restaurants, hotel
lobbies, and railroad station waiting rooms. That
element of the consuming public which considers
programs coming over an electrical circuit so
superior to radio reception that it is waiting for
the coming of wired wireless is not, and never has
been, a prospect for radio sets.
We believe our contemporary has considerably
exaggerated the possibilities of wired wireless.
The radio industry has little or nothing to fear
from its competition. Wired wireless will serve
a field peculiar to itself and has a valuable mission
to perform but, in so doing, it will not be a serious
or dangerous competitor to the radio industry.
Congress Dabbles with the Radio
Situation
CONGRliSS has been intensely busy tin-
kering with the radio situation during
the last few months. The House Com-
mittee on Marine and Fisheries, the Senate
Committee on Interstate Commerce, and the
Senate Patent Committee have been the scene
of endless hearings, inquiring into every phase
of broadcasting and radio manufacturing. The
result, at the time of writing, has been to paralyze
the Federal Radio Commission into almost
complete inactivity and to confuse the entire
situation with a riot of rabid opinions.
It is likely that some form of legislation will
be passed by the time this editorial appears,
presumably extending the life of the Radio Com-
mission for another year. The opposition to this
course is based largely on a desire to embarrass
Secretary Hoover with the radio situation by the
automatic operation of the unamended Radio
Act of 1927. If the situation does revert to his
jurisdiction, he must make some progress with it
and. in so doing, will incur the enmity of poli-
ticians in the areas affected. Thus Congress,
unable to help the radio situation by intelligent
legislation, proceeds to use it to its own political
advantage.
Nothing of particular novelty has been re-
vealed in any hearings and only one statement of
importance has been made A bill has been pro-
MAY, 1928
RADIO PICTURE AND TELEVISION PROGRESS
11
posed to clarify the equitable distribution of
broadcasting service clause of the Radio Act of
1027 The total wattage of broadcasting stations
in the southern district is less than that of the
largest single station in the northeastern district.
The Federal Radio Commission is being blamed
for this situation and is charged with discrimina-
tion against the south. To bring about a modi-
fication, the bill proposes that the total wattage
of the five districts shall be equalized.
Commissioner Caldwell responded to this
destructive suggestion by pointing out that the
principal program sources of the entire country
would, by the operation of such a provision, be
required to suffer substantial power cuts, de-
priving immense rural populations of their favor-
ite program services. There are neither stations
nor frequency space sufficient to bring up the
total wattage in the less progressive areas (speak-
ing only from the broadcast transmission stand-
point), and, consequently, the only possible way
in which to observe the proposed law would be
to reduce the power of every station in the New
York district by eighty per cent., or eliminate
a large number of medium and high-power
stations. Many of the politicians were highly ir-
ritated by Commissioner Caldwell's succinct
exposition of the situation but, so forceful was his
logic that the only answer, so far made, has con-
sisted of pointed and — it seems to us — unjusti-
fied insinuations about the Commissioner's
susceptibility to the influence of the great broad-
casters.
Commissioner Caldwell is to be commended
for stating the facts so plainly and having the
courage, at this time, to stick to the truth even
though it be favorable to the viewpoint of the
\. B. C. Political wisdom dictates a different
attitude but he is swayed only by a desire to
serve the listener.
The only other activity of the Commission
has been the issuance of a formidable list of fre-
quency and power changes by Commissioner
l.aFount, affecting stations on the Pacific Coast.
These changes promise to clear up many existing
heterodynes. It seems quite apparent, at this
writing, that congressional bungling will prolong
the present unsatisfactory radio situation for
another year.
HAIKU ThLEVISlON APPARATUS ON SALF-
1)RFSS dispatches from London announce
that Selfridge's is selling Baird television
outfits at a price of thirty-two dollars per set.
Investigation reveals, however, that this equip-
ment consists only of the parts for building a
shadowgraph transmitting outfit. The amateur
transmitting enthusiast can send, at his home, ;i
moving hand or a shadow made by a cardboard
figure held before the outfit. The cost of the
receiver parts, to be marketed later, will be ap-
proximately the same. The shadowgraph offers
a field for entertaining home experiments and it
should promote interest in the problems of tele-
vision.
As to the commercialization of television in the
United States, a statement made by David
Sarnoff of the Radio Corporation of America,
before the New York Electrical League, is
significant. He is quoted in the press as saying:
"We will hear much more about these develop-
ments within the next year. My guess is that,
within five years, they (television receivers) will
be as much a part of our life as sound broad-
casting is now."
An unnamed representative of the R. C. A.
is quoted in the New York Times, when ques-
tioned as to how soon the Alexanderson still
picture transmission apparatus will be placed on
the market, as follows: "Oh. it will be a long
•*-Ua
.-•-.-.,
-
GERMAN POLICE USE THE KORN
PICTURE SYSTEM
In recent months, the Korn picture transmitting
system has been adopted for regular use by the
German police. The illustration shows a sample
of the received picture. Average transmitting
time for a picture is said to be 2j minutes
time. Look at the apparatus. It is top cumber-
some. It is only in experimental form."
Considering the great number of years that
photo transmission has been the subject of ex-
periment both here and abroad and the success
obtained by such pioneers as Korn, Jenkins
and Baird, and the recent successes of the Bell
Laboratories and Alexanderson, it is surprising
that picture broadcasting is so slow in becoming
a supplement to tone broadcasting.
PICTURE BROADCASTING MUST CONTAIN NO "ADS"
MR. DAVID CASEM, Radio Editor of the
New York Telegram, pointed out editori-
ally recently that numerous commercial broad-
casters are already considering ways and means
in which they can use picture broadcasting. He
points out that, if picture transmission is used to
distribute miniature billboards in the home, its
growth will be stifled at the outset. The public
is not going to buy picture receiving apparatus
in order to have itself exploited by advertisers.
Mr. Casern's point is well taken. Picture
broadcasting must adhere to the highest stand-
ards of education and entertainment, if it is to
be popularized. We have interviewed many
broadcasting station managements on this sub-
ject, and have found that this fact is generally
appreciated. Program managers have apparently
learned that the first and most important factor
to be considered in any radio presentation is that
it shall please the radio audience. To this rule,
picture broadcasting is no exception.
ANNUAL REPORT OF THE R. C. A.
TpHE1 annual report of the Directors of the
* Radio Corporation of America to stock-
holders, for 1927, indicates a substantial im-
provement in the corporation's financial position.
The net income transferred to surplus amounts
to §8,478,320, as compared with $4,661,397 for
the previous year. About seven per cent, of its
gross business is the result of its transoceanic
services, the need for which inspired certain naval
officials to encourage the company's original
formation. Its combined transoceanic and marine
business is but nine per cent, of its total business.
It collected, during 1927, $3,310,722 for royal-
ties, of which about one and a third million cover
past damages. An interesting item among its
assets is nearly ten and a half million dollars in
accounts receivable. It is not generally considered
that this is largely inventory and it may be
mostly uncollected royalties. Although more
than three million dollars were collected as
patent royalties, a good part of the surplus has
been devoted to reducing the value of the patents
credited in the balance sheet. They are now down
to a little over five and a half million.
THOSE interested in studying sales and dis-
tribution figures will find the report com-
piled by the Electrical Equipment Division of
the Bureau of Foreign and Domestic Commerce,
aided by N. E. M. A., on stocks of radio equip-
ment in the hands of radio dealers, very illumi-
nating. This is the second of a series of quarterly
reports to be issued. A little over 30,000 dealers
contributed to the information. On October t,
the dealers had 65.921 battery sets in stock and,
THE KORN SYSTEM OF RADIO PICTURE TRANSMISSION
Doctor Korn (extreme right) demonstrating his latest transmitter to German police officials. Syn-
chronism is achieved by synchronous motors and the received picture is made on light-sensitized paper
revolving on a drum in a light-proof chamber. It is said that the armies of Italy and Japan use the
Korn "telautograph" which enables aeroplane observers to draw simple maps and then radio them
direct to their bases
12
RADIO BROADCAST
MAY, 1928
on January i, the number had fallen to 62,778.
The total stock on hand averages but two per
dealer, a number insufficient to cause uneasiness.
Here and There
THE Association of National Advertisers
has appointed a committee to make a survey
of broadcasting as an advertising medium. They
will endeavor to ascertain the average audience
listening to a radio program. Their task is
equivalent to determining the number of crickets.
chirping at any given instant, in a swamp, on a
foggy summer evening.
LIEUTENANT Commander Craven has been
assigned to the Federal Radio Commission
by the Navy Department to grapple with the
short-wave problem.
ALTHOUGH it is definitely known that
both the N. B. C. and the Columbia chains
will have microphones at the political conven-
tions, just how these events will be handled is
not yet made clear. Both chains have commit-
ments to commercial broadcasters and any alter-
ations to their schedules are made at the price of
commercial income. Mr. Aylesworth of the
N. B. C. has pointed out these difficulties and
issued a general hint through the press that the
entire convention proceedings might be spon-
sored by one commercial broadcaster. It appears
that there was no great rush of volunteers as a
result.
STATION WOAI, San Antonio, Texas, re-
cently joined the N. B. C. network. It
had been one of the few independent stations
assigned a cleared channel by the Federal Radio
Commission. The Commission has no control
over the programs radiated by a station and is
not in a position to require that an independent,
assigned to a cleared channel, shall not use chain
programs after receiving such an assignment.
ASST. Secretary of Commerce for Aeronautics
William C. McCracken, Jr., announced
that. approval had been obtained for the erection
of a radio control station at Key West to be
operated by the Airways Division of the Light-
house Service. It will provide and exchange
weather information between terminal airports,
radio communication to aircraft in flight, and a
radio direction service.
THE transatlantic telephone service has been
subjected to a forty per cent, cut in rates,
reducing the basic rate from New York to Lon-
don to $45 for three minutes and $15 for each
succeeding minute. The hours of service have
been extended to from 7:30 A. M. to 8 P. M.
Eastern Standard Time, corresponding to 12:30
p. M. to I A. M. in Great Britain. The service to
Berlin, Hamburg, and Frankfort was inaugurated
on February 10, and to Sweden on the 2oth.
THE Department of Agriculture is extending
its broadcasting service through NAA,
Arlington, by issuing weather reports on several
frequencies, both in telegraph and voice. The
new schedule will benefit aviation and agricul-
ture in particular.
OFFICIAL reports of American exports of
radio apparatus in November indicate
their aggregate value to be about one and a
quarter million dollars, with Canada, Argentine,
Australia, and Uruguay the largest purchasers,
f f f A CHINESE broadcasting organiza-
tion has been formed which will rent time from
a radio telephone plant at Shanghai. A subscrip-
tion of ten dollars a year is to be charged each
Estimated Number of Radio Receivers in Use
United States, January 1, 1928
'"pH ROUGH the courtesy of the radio division, National Electrical Manufacturers'
A Association, the figures showing the number of radio sets now in use are presented.
New York, California, and Illinois, are the leaders in order, according to this survey.
Note the number of estimated sets in the southern states, figures which are interesting,
in view of the efforts of some Congressmen, especially from southern states, to have an
"equitable station-power distribution" clause made a part of the present radio act.
STATE
Alabama.
Arizona ....
Arkansas
California .
Colorado
Connecticut
Delaware
District of Columbia
Florida
Georgia ....
Idaho ....
Illinois ....
Indiana ....
Iowa ....
Kansas
Kentucky
Louisiana
Maine ....
Maryland
Massachusetts .
Michigan
Minnesota .
Mississippi .
Missouri
Montana
TOTAL SETS
45,000
25,000
42,000
704,000
89,000
125.000
15,000
44,000
73,000
64,000
26.000
539.000
184,000
176,000
104,000
46,000
74,000
39,000
56,000
328,000
336.000
129,000
28,000
227,000
29,000
STATE
Nebraska
Nevada .
New Hampshire
New Jersey .
New Mexico
New York .
North Carolina
North Dakota .
Ohio ....
Oklahoma .
Oregon .
Pennsylvania
Rhode Island .
South Carolina .
South Dakota
Tennessee .
Texas . . .
Utah . . .
Vermont .
Virginia
Washington
West Virginia .
Wisconsin .
Wyoming
TOTAL
TOTAL SETS
118,000
15,000
25,000
209,000
18.000
876.000
48.000
35,000
464,000
104,000
121,000
501.000
53,000
22,000
41,000
52,000
188,000
33,000
19,000
56,000
217.000
50,000
169,000
20.000
7,000,000
member to meet the cost of providing programs
and employing announcers, Iff THE
MUNICIPAL authorities of Buenos Aires are plan-
ning to extend the service of their station, LOS,
in the Colon Theatre, which has so far been used
exclusively for broadcasting operas and concerts
from the stage of the theatre, f \ | THE
NUMBER, of licenses in the Australian broadcast-
ing system has now reached 300,000. One high-
power station has been erected in each capital
city, and in Melbourne and Sidney there are
two. Telephone lines for interchange of programs
are frequently used. I f f A CONTRO-
VERSY rages as to radio concessions extended
by various Chinese administrations. Japan has
an agreement, negotiated by the Chinese Minis-
try of the Navy, which gives it a monopoly for
thirty years. In 1921, the Federal Telegraph
Company made a contract with the Chinese
Ministry of Communications for five stations to
be operated by the American company for
twenty years. The British also obtained con-
tracts on behalf of the Marconi Wireless Tele-
graph Company. Apparently an exclusive license
in China is non-exclusive. J f I IN
EUROPE, the International Radiophone Union
regulates the frequencies and time assignments
of broadcasting stations. The Hungarian Govern-
ment has been barred from admission to this
organization at the plea of Czecho-SIovakian
delegates. The Hungarians have been accused
of using their stations to spread propaganda, at-
tacking the Treaty of Trianon, thereby, en-
dangering the integrity of Czecho-SIovakia.
I f I ALL EXISTING telegraph records
were broken during the Christmas season in
England when the inter-empire beam radio
telegraph system transmitted no less than 31,694
Christmas greetings from Great Britain to the
dominions at a speed of 400 words per minute,
withoutasinglerepetitionbeingrequired. ? I t
GERMAN POLICE systems have adopted the Korn
system of picture transmission which is built
along lines which have become conventional.
Korn is a pioneer in the field, having, as early as
1907, transmitted newspaper photographs be-
tween Paris and London. Synchronous motors
and neon lights are used.
THE PATENT SITUATION
IN A decision released February 18, the Dis-
trict Court for Delaware held that Clause IX
of the Radio Corporation of America license
agreement with radio set manufacturers con-
stituted an unfair method of competition in
violation of the Clayton Act. Clause IX of the
license agreement required that each set made
under license be equipped with a complete com-
plement of R. C. A. tubes, sufficient to make
them initially operative. A suit for $10,000,000
damages was subsequently brought by a group
of independent tube manufacturers who avowed
that the operation of this clause virtually
paralyzed their business. Section III of the
Clayton Act specifically provides that its pro-
visions shall apply whether the article, in behalf
of which unfair methods are employed, is pat-
ented or not.
In a suit brought by the Westinghouse Com-
pany, under the Armstrong patent, against the
Tri-City Radio Company, the effect of continued
acquiescence and acceptance of royalties on cer-
tain regenerative sets sold prevented the collec-
tion of damages. The Tri-City was. a licensee
under the Armstrong patent prior to its acquisi-
tion by the Westinghouse Company. It ap-
pointed a sub-manufacturer to make the goods
for it, although the original license did not per-
mit such sub-manufacture
— E. H. F.
A SHORT-WAVE RECEIVER FOR ii.i TO 119 METERS
THIS article describes the construction of a
single-tube receiver and coils to go with it
to cover the frequency band between 1 .37
and 26.7 megacycles ( 1 1 .2 to 2 1 9 meters approxi-
mately) .The receiver may be used with any audio
amplifier system.
It is completely shielded in a copper box ioj'
wide, 9!" deep, and 6" high. The copper sheet
from which the box is made is h" thick. All
joints are soldered and the top opening of the
box is reenforced with \" by \" by ,',," angle
brass which is soldered to the copper. Holes are
drilled in the angle brass for \" 8-32 machine
screws with which to fasten on the cover. The
screws are soldered into the angle brass. The
cover is of sheet copper reenforced at the edges
and center with a strip of brass i" wide by TV'
thick. Holes are drilled in the strip around the
edge of the cover to allow the cover to fit down
on the angle brass where it is tightly held by
hexagonal nuts. Although it takes a few moments
to remove and replace the cover when changing
coils, this method of shielding has been found
to be very complete and mechanically strong.
The copper box is screwed to a 10" by 1 1 J" by
A" wood baseboard to which is also fastened by
three wood screws the 7" by 12" bakelite panel.
The only objects on the panel are the tuning
agd regeneration controls and the output bind-
ing posts. Note that the copper box is not cen-
tered behind the baseboard but is set in \" from
the left-hand edge of the panel in order to allow
room for the output binding posts at the right.
At the rear of the set there is a bakelite strip
on which are mounted four binding posts for con-
nections to the antenna, A battery, and to the de-
tector positive terminal of the B battery. The
three battery wires go into the copper box
through one hole and the antenna lead through
another. Most of the parts are mounted on an
inside baseboard loj", by 8^", by A" thick.
As will be seen by reference to Fig. I, the an-
tenna is coupled to the antenna coil through a
General Radio midget variable condenser of
15-mmfd. capacity, C,. A General Radio coil
mounting holds the plug-in coils and is spaced
a generous distance from the sides of the box.
The tuning condenser, C3, is a Cardwell of 50-
By Lloyd T. Goldsmith
Col. E. H. Green Radio Rnrarch
A "Super" for Code Work
THE short-wave receiver described in this article
has been designed for use with any ordinary
audio amplifier, and when so used, will be found
extremely sensitive, especially for code reception.
The main purpose for its design, however, is its
adaptation to the super-heterodyne unit described
on the pages following those devoted to the present
article. The super-heterodyne combination will
not be satisfactory for short-wave phone reception
due to the peaked characteristics of the intermediate-
frequency amplifier. It will, on the other hand, be
wonderfully sensitive for code reception.
— THE EDITOR.
7Ant.
mmfd. capacity of the straight frequency-line
type. The regeneration condenser, C2, is a Na-
tional of 250-mmfd. capacity. The latter two
condensers are mounted directly on the copper
box and bakelite panel. Each is provided with a
4" National Velvet vernier dial.
The grid condenser, C4, is a loo-mmfd. San-
gamo across which is a Tobe 8-megohm grid
leak, Ri. The detector tube is a UX-2OI-A and
fits in a General Radio ux type socket mounted
on a General Radio rubber cushion to absorb
shocks and reduce noises. The leads to the socket
are of flexible rubber-covered wire. The radio-
frequency plate choke, U, is a Samson No. 85
of 85 tnh. inductance The audio-frequency
choke, U, in the positive B-battery lead is a
Samson No. } of 3 henrys inductance. The audio-
~l
- I
A
FIG. I
Circuit diagram of the short-wave receiver described in this article
13
14
RADIO BROADCAST
MAY, 1928
frequency current is bypassed to filament through
a i-mfd. Tobe condenser, C6, which in the
photograph can be seen mounted on the base-
board beneath the regeneration condenser. The
copper box is grounded to the positive A binding
post.
No rheostat, filament switch, or voltmeter is
provided on the receiver because it is designed
primarily to be used with the screen-grid tube
super-heterodyne described in the article follow-
ing this one in this same issue, and common A
and B batteries are used, the A battery connec-
tions for the receiver being taken off the filament
terminals of the second detector socket of the su-
perheterodyne. In this way the filament switch
on the super-heterodyne controls the filaments of
all the tubes, and the voltmeter reads their fila-
ment voltage, which is adjusted by the master
rheostat.
The plug-in coils are mounted between J"
bakelite strips provided with General Radio type
274-1' plugs. The socket, or base, into which the
coils are inserted, is a General
Radio 274-8 base, which retails
complete for $t.oo. The plugs on the
coils must be so spaced that they
will plug into this standard base.
The tickler is mounted next to the
antenna coil when it is of the same
diameter as the latter, but in the
larger coils, to save space, it is
mounted within the secondary coil.
In any case, the tickler should be at
the filament end of the secondary
coil.
The coils are wound on a bakelite
tube which has been cut in half
diametrically and held together by
SKCLONDARY (.on.
1 K.KM-R (]oil.
HASPS
No. of
7'urnj
Diameter
(Inches)
.Site of
Wire
(D.C.C.)
No. of
7 urns
Diamflfr
(In, /'fit
Site of
Wire
(D.C.C.)
I'Tfquerttv
(Megacycles)
Wavelenftb
(Meiers-
dppTOX.^
4
18
1
I
16.7 -26.7
.8 -11.2
7
18
4
11.5 -18
26. 1-16.7
i i
18
6
8.3 -13.3
36.2-22.6
t»
18
10
i
6. - 9.4
50 -31.9
U
23
\
18
) }
16
4.2 - 6.52
2.87- 4.6
71.4-46
104.5-65.2
}7
18
10
1
2.1 - 3.33
143 -go
54
,
22
!
2
' IT i '~
219 -138
A TABLE OF COIL SIZES
-Bakelite Tubing
' Brass end Ring
HG. 2
Constructional deta Is for the coil form
C1
L3
L4
Comp ete details of the number of turns for the secondary coil, Li, and
the tickler coil, l.:, for various frequencies are incorporated in this table
Brass Ring drilled & tapped
Machine Screw brass end rings. Kig. 2 shows the con-
struction of the coil form. The desired
number of turns is wound on the form
and given two light coats of collodion.
When the coil is dry the screws are
removed from the end rings, the latter
are slipped out, and the bakelite
form is pushed together so that the
coil can be slipped off. The inside of
the coil is then given a coat of
collodion to add to its mechanical
strength.
The accompanying table gives data
on the number of turns, size of wire,
diameter of the coil, and the fre-
quency band covered with the tuning
condenser used. In the front view of the receiver
are shown the 1 75-meter coil, the 8o-meter coil,
and the 2o-meter coil, while the interior view of
the set shows the 40-meter coil in place.
Elaborate constructional details have not been
given in this article for it is felt that those in-
terested will be sufficiently versed in the art of
amateur set construction to build the receiver
from those data presented. The layout of appara-
tus can be distinctly followed by reference to
the photographs, and the circuit diagram is
so simple as not to require an elaborate ex-
planation.
The receiver as described is complete and
ready for operation with any audio amplifier.
It was primarily designed, however, for code re-
ception, and particularly to be used in conjunc-
tion with the super-heterodyne unit described in
the article beginning on the next page.
I he following parts are required for the single-
tube receiver described:
AN INTERIOR VIEW OF THE RECEIVER
The parts are numbered for cross reference to the list of parts in the column immediately to the right
LIST OF PARTS
Ci — General Radio ij-Mmfd. Midget Variable
Condenser
Cj — Cardwell jo-Mmfd. Variable Condenser
Q — National 25O-Mmfd. Variable Condenser
Q — Sangamo [oo-Mmfd. Fixed Condenser
Ci — Tobe i-Mfd. Fixed Condenser
RI — Tobe 8-Megohm Grid Leak
LI, L2 — Plug-in Coils (Specifications in Text)
L3 — Samson No. 85 Choke
L« — Samson No. 3 Choke
General Radio ux Tube Socket
Six Eby Engraved Binding Posts
General Radio No. 274-8 Coil Mount
General Radio Rubber Socket Cushion
Two 4" National Velvet Vernier Dials
7" x 12" x ,Y' Bakelite Panel
10" x 1 1 5" x |'e" Wood Baseboard
io\" x 8£" x T6e" Wood Baseboard
a1/' Copper Box with Cover lof " x gj" x 6"
Brass Angle, Brass Strip, Angles, etc.
TWO SCREEN-GRID TUBES ARE USED IN THE INTERMEDIATE AMPLIFIER OF THIS SUPER-HETERODYNE UNIT
The unit has been devised for use with an existing short-wave receiver (such as that described in the previous
article), converting it into a remarkably efficient short-wave super-heterodyne, especially suited for code signals
A Superheterodyne for Short- Wave Code Signals
By Lloyd T. Goldsmith
THE standard receiver used for short-wave
code reception usually consists of a detector
(such as that described in the preceding
two pages) and one stage of audio-frequency am-
plification, although sometimes a second audio
stage is used in an effort to secure more volume.
In the latter case, unless a selective amplifier is
used, the noise level is amplified in about the
same proportion as the received signal, which is
undesirable, as the real aim is to amplify the
signal and not the noise. This difficulty suggests
that the signal be amplified at a radio frequency
rather than at an audio frequency in an effort
to amplify it more than the noise background.
Radio-frequency amplification at very high radio
frequencies has not been found very satisfactory
but if the signal be changed to a radio frequency
of the order of 20 to 100 kilocycles, amplification
is not only satisfactory for the signal gain alone
but from the point of view of increasing the signal-
to-noise ratio. T his is what is done in the super-
heterodyne. In addition, if the radio-frequency
amplifier stages are sharply tuned, the selectivity
of the receiving apparatus as a whole is very ma-
terially increased.
With the increase in the number of trans-
mitting stations operating on the shorter waves
the need is becoming greater for a receiver giving
all possible practical selectivity. In an attempt
to realize these requirements the super-hetero-
dyne described in this article was built.
Super-heterodyne receivers using 2OI-A type
tubes with impedance-coupled and tuned trans-
former-coupled intermediate-frequency ampli-
fiers built and tested at the Massachusetts Insti-
tute of Technology have been found very much
worth while in the reception of long-distance
short-wave telegraph signals. Upon obtaining the
new screen-grid tubes, a super-heterodyne was
constructed at the Institute using these tubes
as the intermediate-frequency amplifiers. The
construction of this receiver is described here.
The arrangement, as will be seen by referring
to Fig. i, consists of two stages of intermediate-
frequency amplification using screen-grid tubes,
a beat frequency oscillator, a detector, and
one stage of audio amplification, using ZOI-A
tubes. The unit as a whole is intended to follow
any short-wave receiver, using the latter's de-
tector tube as an autodyne frequency converter,
and changing the signal frequency to 50 kilo-
cycles. The super-heterodyne unit is particularly
adaptable to the. short-wave circuit described on
the previous two pages.
The first intermediate-frequency stage has a
tuned transformer input circuit. The trans-
former, T, has an air core and is a spool made of
\" diameter bakelite having a winding space
-J" wide by j" deep. The secondary winding con-
sists of 1000 turns of No. 28 d.c.c. wire. Over this
are placed a few layers of paper to prevent pos-
sible grounding of the two windings. Over the
paper the primary is placed, consisting of 250
turns of the same wire. The secondary can be
tuned to an intermediate frequency of 50 kilo-
cycles by means of a 5OO-mmfd. variable con-
denser or to 30 kilocycle? if an additional fixed
capacity of 1000 mmfd. is shunted across the
variable condenser.
\\ith a given plate voltage the voltage ampli-
fication of the screen-grid tube is directly pro-
portional to the effective impedance which can
be built up in its plate circuit. (See "Characteris-
tics of shielded-grid Pliotrons," by A. W. Hull
and N. H. Williams, and "Measurements of High-
l-requency Amplification with Shielded-lirid
Pliotrons," by A. W. Hull. Both of these papers
appeared in the Physical Review, April, 10,26,
Vol. 27.) this fact should be kept in mind when
choosing values of inductance and capacitance
to be used as a coupling impedance. In this case
the coils, L, are No. 85 Samson choke coils which
can be tuned from 20 to 50 kilocycles by a 500-
mmfd. variable condenser. Honeycomb coils
15
were tried as coupling impedances and slightly
greater amplification was obtained, but because
of the ease of mounting and compactness of the
Samson choke coils, they were used in the final
receiver. These chokes are helical wound and
although their direct-current resistance is higher
than that of a honeycomb coil having the same
inductance, their effective resistance at radio
frequencies is much less.
The variable condensers are provided with
insulating shafts to keep the .radio-frequency
circuits as far away from the panel as possible
and all except the first are mounted on the shields
with insulating pillars. The interstage coupling
condensers, Q, are of 2ooo-mmfd. capacity and
the grid leak, Ri, is of 100,000 ohms. The B-
battery voltage is 135 volts and the screen-grid
voltage is 67.5 volts.
The filament voltage is reduced to 5 volts by
means of a 2-ohm master rheostat in the positive
A-battery lead and the filament voltage of the
screen-grid tube is further reduced to 3.3 volts by
15-ohm fixed resistances, R, placed in each of
their negative filament leads. The grid returns
are brought to the battery sides of these resist-
ances giving a grid bias, equal to the drop in the
resistance R, of approximately i .7 volts negative.
For grid detection in the second detector the
grid condenser is of 2ooo-mmfd. capacity and the
leak can be from 4 to 8 megohms where the plate
voltage is 45 volts. Provision is made for a C
battery if plate detection is used.
A small amount of regeneration or resistance
neutralization is introduced into the plate cou-
pling impedance of the second intermediate-
frequency stage to secure increased amplification
in that stage. The effective shunt impedance of
the parallel circuit, consisting of the plate coil
and condenser, is limited by the resistance of
the circuit. The introduction of regeneration re-
duces this effective resistance, giving a greater
effective impedance in the plate circuit, with
16
RADIO BROADCAST
MAY, 1928
correspondingly increased amplification. (See
"Complete Suppression of a Single Frequency
by Means of Resonant Circuits and Regenera-
tion," by J. A. Stratton. Journal Optical Society
of America. Vol. 13, No. i, July 1926.) Regenera-
tion is accomplished by means of a small tickler,
L2, in the detector plate circuit of 25 turns wound
directly on the plate coil of the second inter-
mediate-frequency stage. The tickler can be cut
in or out as desired by means of a switch, K,
mounted on the front panel. The receiver was
not designed for broadcast reception and with
air condensers to tune the intermediate-fre-
quency stages, the tuning is too sharp for quality
reception. If, however, fixed condensers of the
proper capacity are used to tune the intermediate
stages, it is probable that the response curve
would include a band 10 kc. wide. The amplifi-
cation would probably be reduced accordingly.
With a 5O-mmfd. tuning condenser across the
secondary of the short-wave detector out of
voltage is then necessary as when receiving
unmodulated signals.
The oscillator is a "shunt feed" Hartley type
the frequency of which is regulated by a variable
condenser of joo-mmfd. capacity in shunt with a
fixed condenser, Cz, of looo-mmfd. capacity for
3o-kilocycle operation, or yjo-mmfd. capacity for
5O-kiIocycle operation. The oscillator coil, LS,
consists of I 500 turns of No. 28 wire wound on
the same kind of spool as is used for the input
transformer, T, the filament tap being made one
third of the way from the grid end of the coil.
Some difficulties were encountered in adding
a stage of audio-frequency amplification as the
separation between a 5O-kilocycle radio-fre-
quency signal and an audio-frequency signal of
approximately 2 kilocycles is relatively small.
To keep the jo-kc. component out of the audio-
frequency circuit a single-section filter having
a cut-off at approximately 5 kc. is used in the
detector plate circuit of the detector. The filter is
stage coupling through the B-battery leads. All
battery binding posts, as well as the output
posts, are mounted on a bakelite terminal strip
at the rear of the set.
The aluminum shields are 5" by 6" by 9"
except the first which was cut down to 4" by
6" by 9". The first shield contains the input
transformer, with its secondary fixed, and varia-
ble condensers. The second and third shields
contain the first and second stages of inter-
mediate-frequency respectively, along with their
associated coils, condensers, etc. The ij-ohm
fixed resistance in the filament circuit of the first
screen-grid tube is within its aluminum shield
while the fixed resistance in the filament circuit
of the second screen-grid tube is mounted at the
rear of the baseboard behind the shields.
The input lead to the first stage is brought out
through the top of the first shield and connects
directly to the control grid cap of the first screen-
grid tube, which projects through a hole in the
r
Output
._v_
FIG. I
The circuit arrangement of the short-wave super-heterodyne unit. The out-
put of the short-wave receiver which precedes the "super" connects to the
two input posts on the extreme left. The first two tubes are the intermediate
amplifiers, and they are followed by the second detector and audio stage.
The lower tube is the beat frequency oscillator
which this amplifier works, the outfit is as selec-
tive as one dares make it. An a.c. note appears
and disappears in one half a division on the
100 division scale of the condenser when
working in the 3- to 4-megacycle (75-100
meter) band.
In the ordinary short-wave receiver employing
a simple oscillating tube as a detector of c.w.
signals, the detector is made to oscillate at a
frequency differing one or two kilocycles from
the incoming signal and the resulting audible
beat is heard in the telephone receivers. In tun-
ing the detector when followed by the inter-
mediate-frequency amplifier described here, the
beat frequency is made an inaudible frequency
of 50 kilocycles, instead of the usual one or two
kilocycles. To reduce this to an audible frequency
an oscillator whose frequency can be varied is
made to beat with the jo-kilocycle intermediate
frequency and give a difference frequency of one
or two kilocycles as desired. The beating oscilla-
tor voltage is fed to the grid circuit of the second
detector tube through the grid leak resistor.The
audible beat frequency produced in the second
detector is then amplified by the stage of audio
amplification. For phone reception the oscillator
tube is removed from its socket as no beating
a simple "pi" section consisting of a 3-henry
choke in the detector plate lead preceded and
followed by 2ooo-mmfd. and looo-mmfd. fixed
condensers respectively. The choke is a Samson
No. 3 which has a small open iron core.
There is nothing unusual about the stage of
audio amplification. The transformer is a Samson
with a 6 to i ratio and there is provided a pair of
output binding posts as well as the usual output
jack. The B-battery voltage is 135 volts and the
grid battery is 4.5 volts.
The baseboard is 23j"by io"by j". The front
panel is of bakelite and is 24" by 7" by •&".
The first three dials tune the intermediate-
frequency stages while the fourth controls the
frequency of the beating oscillator. All the dials
are 4" National Velvet Vernier dials. At the right
there is provided a Weston double-range volt-
meter to read plate and filament voltages while
below it are the 2-ohm master rheostat, filament
switch, and output jack. The regeneration switch
is between the third and fourth dials and is a
Yaxley jack switch of the single-pole double-
throw type. The two input binding posts are at
the extreme left of the panel. Plate-voltage leads
are provided with Samson 3-henry chokes and
i-mfd. bypass condensers to prevent inter-
top of the shield. The output lead of the first
amplifier stage is brought out through a hole in
the top of the second shield and connects with
the grid cap of the second shield grid tube, which
projects through a hole in the third shield. To
prevent pick-up by these leads they are wrapped
in copper foil which in turn is grounded. This
aids in the prevention of oscillation in the stages
and helps materially in securing stable operation.
The tube sockets are raised on blocks of wood in
order that the control grid may project as far
as possible through the hole in the top of the
shield. The grid terminal is insulated where it is
likely to come into contact with the edge of the
hole and the grid lead is wound into a spiral
spring which makes a tight connection to the
grid terminal.
The last shield, placed at right angles to the
first three, contains the audio beating oscillator.
All the shields are connected together and
brought to a binding post at the rear of the set
marked "Ground." In this way effects of ground-
ing the shields individually or collectively, the
negative A alone, or shields and battery together,
may be noted. Behind the oscillator shield there
is the detector, filter, and the stage of audio am-
plification.
MAY, 1928
A SUPER-HETERODYNE FOR SHORT-WAVE CODE SIGNALS
17
400
350
300
o 250
o
c:
200
VOLTAGE AMPLIFICATION
SINGLE STAGE R.F. AMP.
A- Screen-Grid Tube
With Regeneration
B- Screen-Grid Tube
Without Regeneration
C-UX-201-A
Transformer-Coupled
D-UX-240
Impedance-Coupled
150
100
49 50 51
FREQUENCY-KILOCYCLES
FIG. 2
Showing the voltage amplification for a single
without regeneration and for different tubes and
EXAMINING THE CURVES
AN EXAMINATION of the amplification
curves of Fig. 2 shows that at 50 kilocycles
the maximum amplification obtained in one stage
with the plate impedance used is 155 without
regeneration and 370 with regeneration. By
amplification is meant the ratio of the voltage
appearing across the plate impedance to the
voltage impressed on the grid. The curves also
indicate the sharpness of tuning of a single stage.
The amplification obtained in both stages of
intermediate frequency is rather difficult to
measure accurately because it is so great but is
in the order of 25,000 with regeneration. The
amplification obtained in the stages of inter-
mediate frequency of other super-heterodynes
built at Massachusetts Institute of Technology
using ux-2Oi-A tubes has been (see Fig. 2) in
the order of 25 for one tuned amplifier stage and
16 for one stage of impedance-coupled amplifica-
tion with high-mu tubes. (These data were
presented in an unpublished report of Green
Radio Research, Massachusetts Institute of
Technology).
A compromise had to be made between greater
amplification secured by increased regeneration,
and sharpness of tuning. In the present arrange-
ment the amplifier is not well adapted to the
reception of voice and music as the width of the
band of frequencies passed in a single stage is
not more than 1400 cycles.
Too much stress cannot be laid upon the need
of proper shielding when using the screen-grid
tube. The grid leads from the tubes must be
shielded from all the plate circuit apparatus of
the same tube. The covers of the shields would
be much better flanged to eliminate cracks after
the cover is put on. The holes for the wires
should be as few as pos-
sible and no larger than
necessary All radio-
frequency circuits
should be kept within
the shields, by the use of
chokes and large bypass
condensers in the plate
circuits particularly.
The amplification
curves were obtained
by the substitution
method using a vacuum-
tube volt-meter. A 50-
kilocycle voltage from
an oscillator is impressed
by means of a calibrated
resistance on the input
of the single stage and a
reading is taken on the
vacuum-tube voltmeter
connected in the plate
circuit of the detector.
Then the stage is cut
out and a second voltage
is impressed upon the
input terminals of the
detector of such a value
as will give the same
reading on the volt-
meter. This input volt-
age will be larger than
when the stage of ampli-
fication is used and if
the current through the
variable resistances is
kept the same in both
cases, the voltage im-
pressed will be directly
proportional to the
corresponding values of
resistance. The ratio of
the value of resistance used without the stage of
amplification to the value of resistance used
with the stage of amplification gives the voltage
amplification of the stage. All measurements are
made with the oscillator tube removed from its
socket and a resistance of 10,000 ohms is placed
in series with the test leads from the calibrated
resistance to represent the plate resistance of the
first detector which is normally shunted across
the primary of the input transformer.
As has been mentioned, the amplifier is for
code reception with any autodyne receiver and
it may either be connected in place of the primary
of the audio-frequency transformer of the re-
ceiver, or more simply by connecting its input
terminals in series with the positive detector B-
battery lead of the receiver.
The operation of the complete receiver is no
more complicated than the operation of the
r.f. stage with or
forms of coupling
usual two-control short-wave outfit. The first
three dials of the amplifier are set at about the
same values and a station tuned-in on the re-
ceiver while the oscillator dial is varied to give
the desired note. The first three dials are read-
justed carefully for maximum volume. Now the
entire amplifier can be left untouched, all the
tuning being done with the tuning and regenera-
tion controls of the short-wave receiver. The
regeneration switch on the amplifier can be used
as a rough volume and selectivity control.
If the receiver described by the author on
pages 13 and 14 is to be operated with the screen-
grid super-heterodyne unit, the following state-
ments hold. Because of the fact that the variable
condenser across the secondary of the input
transformer of the super-heterodyne unit is
mounted directly on the aluminum shield, the
ground post of the shields of the super-hetero-
dyne cannot be directly grounded to the positive
A battery but can be done so through a i-mfd.
fixed condenser. This is necessary because the
copper shield of the receiver is necessarily
grounded to the positive side of the A battery
while the first aluminum shield of the "super"
has been connected to the negative side of the
battery. When using the two sets together, then,
the positive side of the A battery is grounded
and the shields of the "super" are connected to
the positive A binding post through the large
condenser.
The following parts were used in the con-
struction of the super-heterodyne unit:
LIST OF PARTS
T — Special Input Transformer (See Text)
TI — Samson Audio Transformer, 6-1 Ratio
L — Two Samson No. 85 Choke Coils
LI — Five Samson No. 3 Choke Coils
U — 25-Turn Tickler Coil (See Text)
U — Special Oscillator Coil (See Text)
C — Four 500-mmfd. National Variable Con-
densers
Ci — Four 2ooo-mmfd. Sangamo Fixed Conden-
sers
Ci — Three looo-Mmfd. Sangamo Fixed Con-
densers
Ca — Five i-mfd. Dubilier Fixed Condensers
R — Two 1 5-Ohm Carter Fixed Resistances
Ri — loo.ooo-ohm Tobe Resistor with Mounting
Ra — 4-Megohm Durham Grid Leak with
Mounting
Ra — 2-Ohm General Radio Rheostat
Five General Radio Sockets
Yaxley Filament Switch
K— Yaxley S.P.D.T. Jack Switch
Carter Midget Open-Circuit Jack
Ten Eby Engraved Binding Posts
Four 4" National Velvet Vernier Dials
White Pine Baseboard 23!" by 10" by J"
Bakelite Panel 24" by 7" by Ty
Aluminum Shields, Extension Shafts. Insulating
Pillars, Angles, Wood Screws, Etc
A PANEL VIEW OF THE SHORT-WAVE "SUPER" UNIT
Despite the number of dials on the panel, the receiver is no more difficult to tune than the ordinary
two-control short-wave receiver. After the dials on the super-heterodyne unit have once been set,
all the tuning is done by means of the controls of the short-wave receiver which precedes the "super"
Ourpur
Condensers
I
b&C
Terminals
R4
R3 UX-201-A UX-171
(CX-301-A) (CX-371
THE SIMPLICITY OF THE D.C. AMPLIFIER IS EVIDENT FROM THIS PHOTOGRAPH
Irrpuh
-A
-A)
By Victor L. Osgood
THE problem of getting really fine tone
quality, power, and volume from an am-
plifier entirely electrically operated from a
1 1 5-volt direct-current supply is one that has
frequently stumped the fan who does not live in
a district where a.c. is available. Many still be-
lieve that it is not possible to do away with B
batteries where the supply is d.c. in nature, and
still get good quality and volume.
The problem for a time was a baffling one, but
the introduction of power tubes, especially those
of the lyi-A type, has made possible the design
of a power amplifier that has won the approval
of all those who have heard it.
The solution lies in combining a stage of trans-
former-coupled amplification with a second stage
of push-pull, using two tubes in parallel on each
side of the push-pull system. Ninety volts are
placed on the plate of the first tube (a ux-aoi-A
About the Amplifier —
THE majority of self-contained electrically-
operated receivers now on the market are designed
to function by plugging into an alternating-current
source. While there are some manufactured receivers
now available for use where the supply is d.c., these
are few and far between. Constructional articles on
d.c. equipment have been equally scarce, mainly due
to the fact that the districts where d.c. is supplied
are considerably in a minority. The combined power
amplifier and power-supply unit described in this
article is especially for the much-neglected con-
structor whose house supply is d.c. It will handle as
much undislorted output as will a single 171 type
tube with 180 volts on the plate and 40.5 volts on the
grid — sufficient for ordinary home purposes.
— THE EDITOR
- Six resistors
in series -14.3 ohms each
B+90 B+67 Det *Jo22%vMBMery B~ V Gnd'
Plate
FIG. I
or a cx-3Oi-A) with a grid bias of 4.5 volts, and
power tubes of the lyi-A type are employed in
the push-pull system with a plate potential of
105 to 1 10 volts and a grid bias of 22.5 volts. The
input connection to the amplifier may be made
directly to the plate of the detector tube in the
receiver itself. Four ux-171-A (cx-3yi-A) tubes
are used in the push-pull system, as shown in the
schematic diagram, Fig. I, and they can supply
an output of 700 milliwatts to the loud speaker.
This will be found ample to give excellent tone
quality and volume. A push-pull amplifier some-
times has a tendency to oscillate and for this
reason a 25,ooo-ohm resistance, R3, is connected
in the center tap lead of the input push-pull
transformer to absorb any unbalance in the cir-
cuit which would otherwise tend to make the
amplifier oscillate. The filaments of the I7I-A
type tubes in the power amplifier are lighted with
power obtained from the 1 1 5-volt line after the
voltage has been reduced by resistance Ri.
The circuit is arranged so that plate potential
for the radio-frequency amplifying tubes and the
detector is available; thus the necessity for B
batteries is altogether eliminated.
Even though the supply is d.c. some filtering is
necessary to eliminate the commutator ripple in
the voltage. The filter circuit used here, however,
is very simple, consisting of one choke coil, L,,
and a 4-mfd. filter condenser, Ci. Two i-mfd.
bypass condensers, G> and C3, are also necessary
across the two intermediate voltage taps. The
d.c. voltage rating of these condensers need not
be more than 160 volts. Either 67 or 90 volts are
available for the plate circuits of the r.f. ampli-
fiers, the choice of voltage depending upon the
individual set and the owner's preference.
Biasing voltages are supplied by dry batteries.
Were we to take the required 22.5 volts C bias
from the power line, we would, of course, have to
deduct just that much from the total voltage
18
THE RIGHT ,W.fk>fUw GO
ATION
By L. W. Hatry
M'
"ANY set builders have searched for the
ideal form of amplification by plodding
their way through combinations of re-
sistance, impedance, and transformer coupling,
attempting to effect a compromise between the
supposed quality of one system and the well-
known high step-up ability of another. Or, at
times, the search for perfection may have been
tinctured with the desire for a combination which
made use of apparatus already on hand.
Whatever the reasons for such combinations,
they should be made only with some apprecia-
tion of the apparatus and its limitations. Many
persons, for instance, wonder where in an a.f.
system to place the audio transformer if only one
is used. The answer to such questions can always
be found. The method is simple.
Consider that the voltage step-up:
(i.) — in a 20 1 -A is 8.
(2.) — in a 199 is 6.
(3.) — through a resistor-coupler is I.
(4.) — through an impedance-coupler is i
(5.) — through a transformer is 2, 3, 3j,
according to the step-up ratio
windings.
(6.)— through a high-mu tube (240 type) is about
20, or through any tube in a resistance- or
impedance-coupled stage ought to be about
two-thirds of the tube's mu (we have taken
the effective step-up to be six in the case of
a 2O1-A type tube).
This information is available in magazines, in
catalogues, in tube instruction sheets, and in text-
books. It allows one to engineer his a.f. amplifier
with the employment of something akin to in-
telligence and the enjoyment of a feeling near
that of competence.
As a preliminary to this engineering feat,
choose some audio system you know to be func-
tioning in a way that satisfies. As an example,
let us use a two-stage amplifier with 3 to I and
6 to i audio transformers, a 2OI-A in the first
5, or 6,
of the
__..^_ r?nrl Thi- Pnv Pi !•*:<•_______
Cr'HE signal voltage handling capacity of a
J. tube used as an audio amplifier is governed
by the amount of bias placed on that tube's grid.
Thus, a 2O/-A type tube, with 4.5 volts bias (and
the corresponding plate roltage of 90) will be over-
loaded and distort if called upon to handle more
than 4.5 peak wits. The following table of C and
B battery voltages for various lubes used as ampli-
fiers will serve to make the author's article more
complete:
TUBE TYPE
B VOLTS
C VOLTS
Mu
45
".5
8.4
67
3
8 4
2O1 -A
90
45
•5
H5
9
8.5
OO
6
7-9
I 12
"35
0
8.2
157
10.5
8.2
00
.6.5
3
I?'
'35
27
2.9
180
40.5
29
90
4-5
7- 5
210
'35
9
/ •>
1 80
10
7-5
222
180
> 5
60
stage, and a 171 in the second stage, as shown in
Fig. i. The power tube is getting a B voltage of
180 and is properly biased so it is important to
remember that its grid-swing limit is about 40
volts peak. To load the power tube, the second
a.f. transformer must supply this 40 volts. We
shall now determine the characteristics of an
amplifier which will fulfill this requirement. For
the second or the final audio transformer to give
40 volts, the grid of the tube in the first stage
must be getting a voltage equal to 40 divided
by the turns ratio of the transformer and the mu
of the tube. The overall gain of the amplifier
in Fig. i will be:
T Vt = zoi-A T
3X8 X 6 = 144
Thus the requisite voltage at the output of the
detector must be: • •
-^ = 0.28 VOLTS
144
For sake of argument we shall accept this value
of 0.28 volts as being average in future calcula-
tions. It has been the writer's observation, how-
ever, that many signals overload the 171 with an
amplifier of this type, which would indicate that
the output voltage of the detector sometimes
exceeds 0.28 volts. This holds true for a set in
Hartford, Connecticut, which, of course, is com-
paratively surrounded with high-powered broad-
casters. If the detector will put out 0.56 volts,
twice that calculated above, we can use a 3 to i
transformer instead of the 6 to i transformer
in Fig. i with somewhat better frequency charac-
teristics.
Presuming that the a.f. amplifier will be satis-
factory if up to the grid of the power tube it has
a voltage multiplying ability of 144, the business
of figuring equivalent combinations of resistance
or other couplings is easy. For instance, in a three-
stage resistance-coupled amplifier, such as is
shown in Fig. 2, using 2OI-A tubes, the gain up
to the grid of the power tube will be (bearing in
mind that a resistor-coupler has a gain of i and
that the actual amplification through the tube
is about two-thirds of its mu):
Re
Vt = 2oi-A
X 6 X
Vt
X
• 201-A Re
6 X i •
If the second tube has a grid bias of 4.5 volts
Del.
FIG. I
FIG. 2
24
RADIO BROADCAST
MAY, 1928
and the correspondingly correct B voltage (in
which case it should not be called upon to handle
more than 4.5 volts signal voltage), it would be
overloaded when required to handle the six volts
which would deliver 36 a.f. volts to the grid of the
final tube. This latter figure is not even enough
to load up a 171 fully. The bias on the second
tube could be increased, with correspondingly
greater handling capacity, but this in turn
would necessitate a higher B-battery voltage. It
will be seen, therefore, that the second 2OI-A
audio tube would be nicely loaded with a 4-volt
grid-swing, in which case it would be able to
supply the final tube with 24 grid volts. A 171
type tube with only 1356 volts and a C bias of
27 will be adequate to handle these 24 volts.
With this amplifier the detector must output
0.67 volt (24 •*• 36) to load the 171, which is
quite a lot, if for no other reason than that local
stations are likely to be necessary for so high a
voltage. It will be agreed, then, that the usual
resistance coupled amplifier with 2OI-A type
tubes is not very satisfactory.
But suppose we use 240 type high-mu tubes
with a working mu of 20. Here are the figures:
Re Vt
i X
240 Re Vt = 240 Re
> X i X 20 X i =400
The 240 will take a grid-swing of 3 (with 180
volts B, 3 volts C). It can overload a 171 on 180
volts if it gets more than 2 grid volts because 2
multiplied by 20 (the gain in the tube) is equal
to 40, the maximum handling capacity of the
171. Hence, if three resistance-coupled stages
are used, and since we have already decided that
an amplification of 144 will satisfy for average
conditions of detector output, the use of 240 type
tubes is probably foolish. By dropping the plate
resistor of the first tube to 100,000 ohms, the
latter's step-up can be reduced to about 12.
That would give an overall step-up of 240 to the
grid of -the last tube. A 2OI-A type tube in the
first stage, with a step-up of only 6, will reduce
the overall gain to 120, which begins to fit better
with the desirable figure.
Now let us consider a single resistance-coupled
stage. There has been a lot said about it in some
of the more active sections of the press:
Re Vt = 240 Re
I X 20 X I = 20
That is obviously no good. Why? The detector
would have to output 2 volts in order to put
40 volts on the grid of the power tube. What
about one resistance-coupled and one transformer
coupled stage, such as that shown in Fig. 3?
T Vt = 240 Re
3 X 20 X i = 60
It will be seen that the gain is insufficient in such
a combination, too great a detector output being
necessary. If, however, the transformer were a
high-grade 6 to i unit instead of a 3 to I unit, the
overall gain would be 120, which is much better.
Now let us consider the following three-stage
a.f. amplifiers, shown in Figs. 4 and 5, in which
Det.
FIG. 3
the second audio tubes will handle about 4.5
volts grid voltage (since they are biased accord-
ingly):
T Vt
3 X
Vt = 201-A
X 6 X
Re
Re
Vt = 2oi-A
X 6 X
Vt = 2oi-A
X 8 X
Re
i = 108
T
3 = 144
the gain of the amplifier, the smaller the detecto/
output voltage necessary to load up the power
tube. Various three-stage combinations, with
their overall amplification, are listed below. The
necessary C voltage for the tubes may be de-
termined by reference to the table on page 23.
In the first case the next-to-the-last tube will be
badly overloaded if the signal is strong enough
to load a 171 to its maximum handling capacity
of 40 grid volts. In practice, of course, the volume
control on the receiver would be turned down as
soon as overloading of the 2O1-A, manifest as
distortion, became apparent, and thus the 171
would be working uneconomically. To deliver
40.5 volts to the 171 the next-to-the-last tube
Re Vt = 240
Re Vt = 240
l X 20 X
Re
400
Re
Vt = 2oi-A
T
Vt =
20 1 -A
T
i
X 8
X
3
X
8 X
3
= 576
Re
Vt = 20
[-A
T
Vt =
201-A
T
i
X 8
X
2
X
8 X
2
= 256
Re
Vt =
201 -A
T
Vt =
= 201-A
T
i
X
8
X
2
X
8 X
3
= 384
Re
Vt = 240
X 20 X
Re
Vt = 201-A T
X 8 X 3 =480
FIG. 4
has to handle 6.75 volts on the grid. If this tube
were given a raise in bias to g volts with 135
plate volts, it would be capable of handling this
voltage without overloading. Merely moving the
a.f. transformer to the third coupling position, as
in Fig. 5, requires that the second audio tube
have a grid- voltage of only 1.68 to produce 40.5
volts on the grid of the power tube.
Judging from the fact that many set owners
find two high-mu tubes highly desirable in a
resistance — or impedance-coupled amplifier, the
opinion that an amplifier step-up of 400 is some-
times useful, seems logical. Of course the higher
From all of the foregoing come a few useful
rules, which may be outlined as follows:
(i.) In a combination of transformer-coupling
with any other type of audio-frequency amplifi-
cation the transformers should be in the last
stages, and the transformer with the greatest
step-up should be in the last one.
(2.) Always make certain that the tube before
the power tube will not be overloaded before the
power tube is fully loaded. To find this out is
merely a matter of simple division or multiplica-
tion.
(3.) When judging the performance of two am-
plification systems, calculate what the overall
step-up for each is before deciding what has hap-
pened.
There are other simple rules that it is good prac-
tice to heed. They may be stated as follows:
(a.) It is always best to require least of the
detector. This is possible when the a.f. step-up
is high.
(b.) High a.f. step-up is no help to the detector
if the volume control follows the detector, and
the less the step-up in the audio end the more
this is true.
(c.) A detector gives greater undistorted out-
put with increased B voltage, within limits.
Operate it according to the needs of your
set.
A $IO,OOO PHONOGRAPH-RADIO COMBINATION
The phonograph equipment is housed at the left and the radio at the right. The panel in the center
contains a distortion meter (reading up to 150 mils.) and special circuit arrangements make it possi-
ble to control the amplitude of the sound by the top knob in this panel, while the control directly
below it regulates overtones. The installation uses a four-stage balanced amplifier rated at 50 watts.
Individual expression in the rendition of phonograph records or radio is said to be achieved through
circuits arranged to vary both musical pitch and overtones without, at the same time, altering quality.
This installation was especially built for La Salle & Koch, of Toledo, Ohio
C If K> THE great American query, "What's
I new?" we are forced to reply this month,
•*- "Not much." It may be merely an off-
season for records. There were all too few likely
looking titles in the advance lists. Perhaps the
phonograph industry, like book publishing,
blooms in full glory but twice a year and in-
between-times puts out only a few pale buds.
No, it isn't quite as bad as that because we did
find nine records of such exceptional merit that
they quite make up for the mediocrity of the
rest. Among the classical output are several
prize-winners: two duets by Gigli and De Luca,
who can always be counted on to be worth while;
two beautiful songs by Sigrid Onegin; choral
work of outstanding quality by the Metropolitan
Opera Chorus; and two instrumental numbers by
the Columbia Symphony Orchestra. Of the pop-
ular stuff there are five better-than-average
records. Ohman and Arden performing Gersh-
win music; Johnny Johnson and His Statler
Pennsylvanians offering another Gershwin num-
ber and on the reverse one of the best songs from
the Connecticut Yankee; a Paul Whitman mas-
terpiece; two good numbers from the orchestra
directed by the Maestro, known to the trade as
Ben Bernie; and, lastly, a couple of unusual
waltzes by the South Sea Islanders. The rest are
so-so.
'S Wonderjul and Funny Face by Victor Arden
and Phil Ohman and Their Orchestra (Victor).
Superb Gershwin music mixed well with Ohman-
and-Arden piano magic and flavored with a bit
of Johnny Marvin's best singing.
Thou Swell and My One and Only by Johnny
Johnson and His Statler Pennsylvanians (Vic-
tor). Tuneful antidotes for that poisonous late-
winter boredom.
Mary and Changes by Paul Whiteman and
His Orchestra (Victor). Whiteman continues to
glorify American jazz.
The Man I Love and Dream Kisses by Ben
Bernie and His Hotel Roosevelt Orchestra
(Brunswick). This record deserves a great big
gold star.
I've Been Looking for a Girl Like You and
Everywhere You Go by Paul Ash and His Orches-
tra (Columbia). For those who crave their jazz
red hot.
Changes and Let's Misbehave by Ben Bernie
and His Hotel Roosevelt Orchestra (Brunswick).
Keeping up with the Bernie tradition of bigger,
better dance music, with the emphasis on dance.
We'll have a New Home and When 'You're With
Somebody Else by Ben Selvin and His Orchestra
(Columbia). Standard fox trots of the snappy
variety dressed up with fancy orchestration.
Tomorrow and I'm Making Believe That I
Don't Care by the Colonial Club Orchestra
(Brunswick). Just like countless other plaintive
waltzes.
Girl of My Dreams I Love You and Sugar
Babe, I'm Leavin'! by Blue Steele and His Or-
chestra (Victor). One more waltz and a noisy
foxtrot with a raucous vocal chorus.
The Man I Love by Fred Rich and His Hotel
Astor Orchestra (Columbia) A good song handled
with no particular merit. For My Baby by Leo
Resiman and His Orchestra. If your doctor has
tactfully suggested that you do more exercising,
get this record. You can't sit still to this number.
/ Ain't Got Nobody and Weary Blues by Ray
Miller and His Hotel Gibson Orchestra (Bruns-
wick). Right you are! The first is an old number
and what's more it is played in the old fashioned
way with lots of brass and much pep. Of the
second — the only thing that's weary must be
the orchestra after it finishes.
When the Robert E. Lee Comes to Town and /
Scream, You Scream, We All Scream for Ice
Cream by Harry Reser's Syncopators (Colum-
bia). If you haven't heard the words to the latter
song the record is worth listening to — once.
Dawn and We Two by The Troubadours (Vic-
tor). Lewis James and F.d Smalle who manipu-
late the vocal refrains and the Troubadours have
between them made a grand record out of two
fairly good musical comedy numbers.
Among My Souvenirs and Keep Sweeping the
Cobwebs Off the Moon by Abe Lyman's Califor-
25
The
^Month's New
'Phonograph
nia Orchestra. (Brunswick). The treatment of
the first is perfectly orthodox which means good.
The second leaves us cold.
Away Dawn South in Heaven and There's a
Rickety Rackety Shack by Frank Black and His
Orchestra (Brunswick), (a) Even if this were
good we wouldn't like it. Not with that vocal
chorus! (b) Something else again; it's good!
That's (That the Lei Said to Me and The Call of
Aloha by the South Sea Islanders (Columbia).
Waltzes that are waltzes.
Poor Litfie and / Love to Catch Brass Rings on
a Merry-Go- Round by Billy Jones and Ernest
Hare (Columbia), a. The Happiness Boys sing
out the old and sing in the new (Ford), b. Not
very good nonsense.
More or Less Classical
Pescatore Di Perle — Del Tempio Al Limitar
(Pearl Fishers— In the Depths of the Temple)
(Bizet) and Cioconda — Enjo Grimaldo, Principe
Di Santafior (En%o Grimaldo, Prince of Santafior)
(Ponchielli). Sung by Beniamino Gigli and Giu-
seppe De Luca (Victor). Week-day words are
inadequate to describe the exquisite beauty of
Recommended New Records
Pescatore Di Perle — Del Tempio Al Limitar
(Bizet) and Gioconda — En^o Grimaldo,
Principe Di Santafior (Ponchielli) sung by
Beniamino Gigli and Giuseppe De Luca
(Victor).
The Blind Ploughman and The Fairy Pipers
sung by Sigrid Onegin (Brunswick).
Die Zauberflote — 0 Isis Und Osiris (Mo-
zart) and Chorus of Courtiers — on Mischief
Bent (Verdi), sung by the Metropolitan
Opera Chorus (Victor).
Bridal Procession (Grieg) and March of the
Bojaren (Halvorsen) played by the Colum-
bia Symphony Orchestra. (Columbia).
'S Wonderful and Funny Face by Victor
Arden and Phil Ohman and Their Orches-
tra (Victor).
Thou Swell and My One and Only by
Johnny Johnson and His Statler Pennsyl-
vanians (Victor).
Mary and Changes by Paul Whiteman and
His Orchestra (Victor).
The Man I Love and Dream Kisses by Ben
Bernie and His Hotel Roosevelt Orchestra
(Brunswick).
Jupiter Symphony (No. 41, Op. 551)
(Mozart) by the State Opera Orchestra of
Berlin, conducted by Richard. Strauss.
(Brunswick).
26
RADIO BROADCAST
MAY, 1928
these duets as sung by this baritone and tenor
from the Metropolitan Opera Company.
The Blind Ploughman (Radclyffe-Hall-
Clarke) and The Fairy Piper (Weatherly-
Brewer) sung by Sigrid Onegin (Brunswick).
An organ accompanies this rich contralto voice
in the first selection and reflects the seriousness
of the song. In the second selection the tinkling
notes of a piano and a flute illustrate the fairy
music of which Miss Onegin sings delightfully
as well as capably.
Lucia: Sextet — Chi raffrena il mio furore (Why
do I my arm restrain?) (Donizetti) Sung by M.
Gentile, D. Borgioli, G. Vanelil, S. Baccaloni,
G. Nessi, 1. Mannarini and chorus. (Columbia).
This imported recording does not do full justice
to the famous musical race in which the soprano
is foreordained to win. The volume is, for one
thing, too great. On the reverse is Somnambula:
D'un Pensiero (No Thought but for thee) by M.
Gentile, D. Borgioli, I. Mannarini, G. Pedroni
and chorus, which is excellent except for the
thinness of the soprano voice.
Die Zauberflote — O his Und Osiris (The Magic
Flute — Chorus of Priests) (Mozart). Sung by the
Metropolitan Opera Chorus with the Metropoli-
tan Opera House Orchestra under the direction
of Giulio Setti. (Victor). This splendid organi-
zation presents a very plausible chorus of priests
who are evidently all superior musicians. And
the very next moment (on the reverse of the
record) they are equally convincing as a Chorus
of Courtiers — On Mischief Bent (Scorrendo Unili
Remola Via) from Verdi's Rigoletto.
My Message and Nocturne by John Charles
Thomas (Brunswick). The same glorious bari-
tone— and you may like the ballads.
Quartet in G Minor Second and Fourth Move-
ments (Debussy). Played by the New York
String Quartet (Brunswick). All the tricks of the
string trade are herein utilized to demonstrate
the beautiful and varied effects obtainable by
two violins, a viola and a cello.
Bridal Procession (Grieg; Op. 19, No. 2) and
March of the Bojaren (Halvorsen). Played by the
Columbia Symphony Orchestra under the direc-
tion of Robert Hood Bowers (Columbia). This
delightfully gay and lighthearted bridal chorus
must have been written for a fairy wedding;
mortals take their weddings more tearfully.
And here is a march that is not impressed with
its own importance but is quite willing to be ex-
uberant and even humorous. But then a march
scored for strings, and woodwinds as well as for
brasses can present these characteristics more
easily than can the fife and drum brigade. The
Columbia Symphony handles both these num-
bers with ability.
All Hail the Record Albums
IT IS just another miscarriage of justice that
somewhere in these United States there walks
a man, unheralded and unsung. The man
in question is the inventor of the album set.
Until he sold his idea to the phonograph com-
panies (we hope he sold it; if he can't have fame
he should at least have royalties) our record
library contained only selections from operas,
gems from operettas, arias, ballads, folk songs,
bits of this, and bits of that. No extended work
could be had in its entirety because, alas, it
could not be fitted on to the limited space af-
forded by a rubber disc, and it had never oc-
curred to the phonographers to distribute one
work of art over several discs, selling them as one
unit. Now, however, we have whole symphonies,
tone poems, and concertos, complete from the
first note to the last. They come on several
records, neatly stowed away in good looking
albums, and accompanied by explanatory book-
lets which invariably are excellent and use-
ful. These musical works are recorded by the
best talent available in this country and in
Europe and the technical work of putting the
notes on the wax is done so expertly that no
iota of tone is missing, no shading is lost.
In the March RADIO BROADCAST appeared a
partial list of the music available in album form.
The list is growing daily.
Mozart's "Jupiter" Symphony
WE HAVE already reviewed one album set,
the Scheherazade Symphonic Suite by
Rimsky-Korsakov, played by the Philadelphia
Orchestra under the direction of Leopold Sto-
kowsky, and recorded by Victor. This month we
A CLOSE-UP OF THE CONTROL PANEL
A bank of three loud speakers is used with this phonograph-radio combination. Each loud speaker
circuit has its own distortion meter, with controls permitting each circuit to be operated at its own
regulated volume. Circuits and apparatus are provided so that the operator can announce the selection
to be played through the entire loud speaker system
praise another symphony, equally beautiful
in an entirely different way, the Jupiter Symph-
ony (No. 41, Op. 551) of Mozart, played by the
State Opera Orchestra of Berlin, conducted by
Richard Strauss, recorded in Europe for Bruns-
wick. It covers two sides of three records and
one side of a fourth, the remaining surface being
given over to the Turkish March (Mozart-Cerne)
played by Vasa Prihoda. The Rimsky symphony
is full of color, warmth, and emotion. It con-
jures up pictures of the Orient with its glowing
colors, shimmering light, sinuous maidens, sway-
ing camels, dancing fakirs, and the spicy smells
of the market place — all the kaleidoscopic ro-
mance of the East. Mozart's symphony, on the
other hand, brings forth no pictures. It lacks the
warm humanity of the Russian music, lacks its
emotion, lacks its color. But it has something
which takes the place of these qualities, a pre-
cise musical style. It is music as pure, unsullied,
and crystal clear as water bubbling from a
spring on a mountain side. It is melodious from
start to finish for Mozart was an expert harmon-
ist. He lived his short life (1756-1791) at a time
when emphasis was placed on form and har-
mony. The symphony was a fairly recent de-
velopment. It had evolved gradually from the
overture, the instrumental introduction to an
opera, and had been given a more or less stand-
ard form by Haydn who was born twenty-four
years before Mozart. This form consisted of
three or four movements, generally four. The
first and fourth were the longer and more es-
sential, and were brisk in tempo. The second
was slower and eminently lyrical, and the third
usually a sprightly minuet. This is the form used
by Mozart in the Jupiter Symphony. The or-
chestra for which he scored the symphony con-
sisted of one flute, two oboes, two bassoons, two
horns, two trumpets, kettledrums, and strings,
and for the second movement he reduced it by
the omission of trumpets and drums. This is a
much smaller organization than the symphony
orchestra of to-day.
It is particularly in the fourth movement, the
loveliest of them all, that Mozart displays his
technical skill, but not ostentatiously. The
beauty and spontaneity of the music conceal the
learning which is its foundation. The design of
the movement is a combination of the sonata
form and the fugue. The sonata form is that
used for first movements of symphonies and
consists of three parts, the Exposition which
sets forth the themes; the Development which
embroiders the themes; and the Recapitulation
which restates the themes. In this movement
Mozart uses four distinct musical ideas. The first
is given out at once by the violins, its four
opening notes being an ecclesiastical melody of
which Mozart made frequent use. A second, and
gayer, phrase follows this; the subject is then
repeated forte by the full orchestra and at the
end of the passage the second idea is introduced
by woodwind and strings. There are sixteen meas-
ures of this, filled with exuberant tone. Next
there is a return to the church theme treated in
the orthodox fugal manner. At length this same
theme is taken up forte by the full orchestra and
at the fourth measure of it there is heard, in
the first violins, the third idea. After a repetition
of the second idea, the fourth idea — the second
real theme — appears in the strings.
From this brief analysis of the last movement
of the symphony you can perhaps derive some
idea of the intricacy of the framework on which
Mozart weaves his beautiful melodies. You will
love these melodies whether or not you under-
stand the construction, but if you follow the
mechanics of the symphony you will arrive at
a more complete understanding and conse-
quent appreciation of the composition.
'Detector
Distortion
MANY TIMES we
have read about radio
receivers so engineered
that the detector did
not overload, or receivers in which the
detector did overload, or some other refer-
ence to distortion due to detector over-
loading. This leads us to ask such ques-
tions as: When does a detector overload?
What does the output sound like when
such overloading occurs? Is it true that a
C bias detector will handle much larger
input voltages without overloading? If
so, how much? The answers to some of
these questions are being sought in the
Laboratory, and as fast as the material
is ready it will be presented in these
columns.
In the meantime, one of our friends
has determined, empirically, that the
average detector begins to overload when
the detector delivers about 15 TU below
i.o milliwatt. What does all this mean,
you will ask?
Let us suppose that a detector has an
output impedance of 30,000 ohms and
that it works into a load of this impedance,
say a resistance or a transformer of proper
characteristics. Fifteen TU below i.o
milliwatt is equal to about 0.03 milliwatts,
or about 30 microwatts. What voltage
across 30,000 ohms will deliver this
amount of power? This is the useful volt-
age, for it is what the amplifier boosts
in value so that the final power tube in the
system will deliver its rated output.
This voltage may be found by extracting
the square root of the product of the power by the
resistance. Or.
•
rom
E = VWoxK = v 0.03X10— »X3",ooo = rvolt
(approximately)
Therefore, a detector which will deliver 30
microwatts to 30,000 ohms without overloading
will produce i.o volt across the input to the
amplifier. It now remains to prove under what
conditions the detector will fulfill these expecta-
tions, and when overloaded, how the average
experimenter can tell it by the sound of the
output.
Has any reader experience in this matter?
<?4 Short-Wave
THE FOLLOWING letter ap-
ropos of short-wave experi-
mental broadcasting and its
reception is interesting: It
comes from C. R. Strange, of Sydney, Australia.
"On the page 'Our Readers Suggest' in the
December RADIO BROADCAST, there is described
'A Short-Wave Converter for any Radio Re-
ceiver' by Perry S. Graffam.
" It will be of interest to your readers to know
that out here in Australia we appreciate your
journal and that several days ago I built this
adapter to plug into my Grebe Synchrophase
which was presented to me by the A. H. Grebe
Company of Richmond Hill, New York, follow-
ing my reception of their station, WAHG, on 314.5
meters.
"An hour after I had finished Graffam's
adapter I was listening to the transmission from
2 LO (London) through the short-wave station
; sw Chelmsford England, on 24 meters, using
the two audio valves of the Synchrophase re-
ceiver and my model- 100 loud speaker. On the
25th (January) I listened wonderfully to this
station for 55 minutes, the volume being audible
some 15 feet from the speaker. Also on the 25th
and last night 1 listened also with wonderful
success; here, some 13,000 miles away, it is rather
thrilling to listen to London broadcasting at
midday such items as selections from Cavalleria
Rusticana, Percy Grainger's pianoforte arrange-
ments, Carmen, and a fine tenor voice singing
'The Sargent Major's on Parade.'
"We surely are in a wonderful age. Televison
will be the next thing for Australia."
THERE HAVE been numer-
Short-Ware ous attempts to convince the
'Broadcasting public and, we imagine, the
Radio Commission as well,
that broadcasting should take place on the high-
frequency (short-wavelength) bands. Let us
look only at the problem of keeping a station on
its assigned frequency which, for sake of argu-
ment we shall assume to be 10,000 kc., or ten
million cycles. Many broadcasters are having
difficulty in keeping their present transmitters
within one-half kc. of their assigned frequency.
What would be their troubles if they worked at
30 meters? Five-hundred cycles in 10,000,000 rep-
resents an accuracy of one part in 20,000, or five-
thousandth of one per cent. At the present time,
a station operating on 1000 kc. must keep its
assigned frequency to within 500 cycles in one
million which represents one part in 2000 or
five-hundredths of one per cent. In other words,
it would be about ten times as difficult to keep a
station on its frequency at 30 meters as it now
is at 300 meters.
We understand the Navy builds short-wave
equipment that must be accurate to within 100
cycles at 30,000 kc. That is, they build a trans-
mitter to this specification, and a receiver to go
with it and the sum of their percentage inaccu-
racies must not be over 200 cycles in 10 million,
or 100 cycles for the individual unit. This repre-
sents an accuracy of one part in one hundred
thousand, or one ten thousandth of one per cent.,
an accuracy 50 times as great as that required
of stations now operating within the broadcast
band. These Navy units, it should be noted,
are designed for code transmission and recep-
tion.
29
The "Equamatic"
System in
England
RADIO BROADCAST
takes pride in quoting
part of a letter from
Louis G. King, whose
system of tuning, known as the Equa-
matic System, was first described in this
magazine. Mr. King has just returned
from Europe and that his trip was success-
ful may be surmised from this part of his
letter: "Recently we have entered into
an agreement with Graham Amplion,
Ltd., for the production of the Equa-
matic System in the British Isles. After
carefully testing radio receivers produced
by the leading manufacturers in all parts
of the world, Graham Amplion, Ltd.,
adopted the Equamatic System." The
system has, in this country, been most
closely associated with receivers designed
by the Karas Electric Company.
MANY TIMES in the
Finding Ore past year or so, the edi-
by Radio tors have been asked
to forward informa-
tion on devices useful in finding ore or
hidden treasure by radio. Up to the
present time it has been impossible to
give any authentic information regarding
such apparatus, and therefore, we are
appealing to the readers of the magazine.
What is wanted is information on methods
and apparatus used, whether using radio
or other electrical apparatus, results se-
cured, and articles published whether in
this country or abroad. This will enable
us to help prospective treasure hunters
toward a financially successful jaunt.
RADIO LISTENERS in com-
<Real Power munities where there is no
firomtvioll2't a.c. power available need not
feel that it is impossible to
secure sufficient power to operate their loud
speakers properly just because they cannot tap
the house lighting system and get high voltages
and considerable plate current therefrom. For
example, two H2-A tubes will deliver consider-
able power without excessive plate voltage or
current — which means that the farmer who has
no power equipment may secure good quality
and plenty of loud speaker power from B batter-
ies, and do it economically. The table below shows
the relative power output and necessary grid a.c.
voltage to deliver this power from a single 171
or two ii2's in parallel. Note that two nz's
in parallel with 157 volts on the plate require
16 milliamperes from the B batteries and deliver
400 milliwatts of power to a loud speaker on
only 10.5 input grid volts while a 171, taking the
same current from 135 volts, requires a grid volt-
age of 27 to produce 350 milliwatts. Two i I2's
in parallel will have an output impedance of
about 2500 ohms which will work very well into
the average loud speaker:
TUBE EH EC IP WATTS
OUTPUT
171 90 16.5 11 .12
135 27 16 .35
157 33 18 .50
180 40.5 20 .65
2—1 12's 90
135
157
4.5
9.0
10.5
8.0 .08
11.6 .240
16.0 .400
SOME TUBES from Sylvanh
Tested Products Co., have been
^Products measured in the Laboratory
recently. The values given
below are the average of six of each type of tube:
TYPE IP n Rp GM EP EG
201-A 2.2 9.2 12330 750 90 -4.5
112-A 7.0 7.5 5160 1450 135 - 9,0
171 19.0 2.9 2240 1300 135 -27.0
30
RADIO BROADCAST
MAY, 1928
EXPERIMENTERS who have
The Screen-Grid installed a single screen-grid
Tube: Selectivity tube ahead of a detector,
regenerative or not, have been
disappointed at the apparent loss in selectivity
of the system, although the gain increases. Let
us suppose that the resonance curve of a single-
stage of r.f. amplification using a 201 -A tube is
as shown in Fig. I . Now let us use a screen-grid
tube in which the gain may be twice as great.
In other words every point of the resonance curve
of Fig. i is boosted twice as high with the result
as shown in B. In any local area, stations are
separated by 50 kc., so that on Curve A the in-
coming signals from a station 50 kc. off resonance
are below the line which represents the arbitrar-
ily chosen signal magnitude beyond which inter-
ference occurs. Now look at Curve B. Here the
5o-kc. signal is up out of the area in which no
interference occurs, and is heard in the back-
ground of the station to which the receiver is
tuned.
Let us call the absolute selectivity factor, the
ratio between the height of the curve at resonance
to the height at 50 kc. off resonance. This factor
for1 curve A is 50 •*• 2.4, or 2.1, and for the curve
B is 100 -t- 4.8, or 2.1 exactly the same. Then, if
the apparent selectivity is defined as the number
of kilocycles off resonance a signal must be be-
fore it is reduced to the non-interfering region,
we see that for the 201 -A example it is 50 kc.
while for the Curve B where the gain is twice as
great the frequency is 70 kc. These figures de-
pend, of course, upon the shape of the resonance
curve.
Each additional stage of 201 -A r.f. amplifica-
tion increases the gain of the receiver and in-
creases the selectivity, but as Professor Hazeltine
has shown in his recent patent, No. I, 648, 808 —
(Nov. 8, 1927) — by properly designing the inter-
stage transformers in such amplifiers, an increase
in selectivity of 50 per cent, can be obtained at a
loss of only 20 per cent, in amplification. In
other words, in a system using successive tuned
stages, relying upon resonance curves for selec-
tivity, there must always be a compromise be-
tween gain and selectivity. Increasing the gain
without increasing the absolute selectivity 'at
the same time, reduces the apparent selectivity.
Although the signal to which the system is
tuned will be louder, so will the background pro-
duced by other stations.
Adding a single stage of screen-grid tube r.f.
amplification under conditions which produce
maximum gain from that tube, decreases the
apparent selectivity too much. Adding an extra
stage, from which we secure maximum amplifica-
tion, will boost the sensitivity faster than the
selectivity is increased, and we are no better off
than before.
In other words, if three stages of ZOI-A am-
plification are needed to secure sufficient selec-
tivity, more than three stages will be necessary
when using screen-grid tubes. This seems to in-
dicate that these tubes will not decrease the
number of effective tubes in a receiver, but will
actually increase that number — so long as we
use the t.r.f. system of tuning.
The answer, if this reasoning is correct, is to
use a different system of tuning. The super-
heterodyne is one solution; perhaps the Vreeland
system described recently in the I.R.E. Proceed-
ings is another. This is a system designed with
the avowed intention of making a response curve
of a receiver flat on top and very steep on the
sides. It is done by using two closely coupled
circuits so that the resonance hump is not a
single sharp peak, but is composed of two peaks
with a dip between. The Laboratory hopes to
present some quantitive data on this system
110
— Level above —
.which Signals
Interfere
150 100 5C 0 50 100 150 2CO
KC. OFF RESONANCE
FIG. I
soon, and in the meantime welcomes comments
on the problem outlined above.
MANY TIMES per month we
Loud hear about some high official
Speaken in this or that radio company
who indulges in a bit of fore-
casting, usually about the future of radio. Among
other trends, to believe these officials, is that
toward greater power which will be handled in the
future radio's amplifier, one executive going so far
as to state that our sets of the future would have
amplifiers turning into our loud speakers at least
ten times as much energy as they do at the pres-
ent time. Judging from what has happened dur-
ing the past few years, one cannot doubt it, for
in the good old days we were satisfied with the
output of a 199, then we needed a 2O1-A to deliver
sufficient power, then the 112, then the 171 and
210 tubes, and now the 250 type. Each of these
tubes delivers considerably more power than its
predecessor, and to jump from a j-watt tube to a
50 waiter represents ten times as much power
output, that is, 10 TU difference.
We are not convinced. Several years ago we
listened to a pretty fair program coming from a
speaker that was 10 TU better than any speaker
now generally available. That is, it required 10
TU less power to get a good healthy sound from
it. This represents the difference between a power
output of 600 milliwatts (i7i-A), and 60 milli-
Watch for the A. C. "Lab" Receiver
TTUGH KNOWLES' article describing the con-
L~L struction of the popular R. B. "Lab" circuit
for a. c. operation will appear in RADIO BROAD-
CAST for June. The completed receiver has been
thoroughly tested in RADIO BROADCAST Laboratory
and has proved very satisfactory indeed. Readers
will recall the complete experimental article ~.n our
April number describing tests in the Laboratory on
the design of this circuit. The June article describes
completely the construction of an a. c. four-tube
"Lab" circuit receiver. Some of its interesting fea-
tures are: Excellent efficiency for four tubes: a. c.
operation, an extra socket and control switch enabl-
ing quick transfer of the audio system to phonograph
pick-up or short-wave tuner unit, and an interesting
volume control.
— THE EDITOR
watts (2OI-A). In other words, when loud speaker
manufacturers are able to build a loud speaker
with a good characteristic that is 10 TU better
than our present loud speakers, we can all go
back to our old 2OI-A tube, our B batteries, and
start all over again.
What are the prospects? We have heard
that the Western Electric Company builds
a loud speaker much more efficient than the
54O-AW, for sale in England only. It does not
have the same tonal range as the 54O-AW and
is cited only as an example of an efficient
loud speaker.
Incidentally, present trends in loud speaker
design are toward moving-coil affairs, elecro-
dynamic units, such as the Magnavox and the
Jensen cones, and the Vitaphone, which is a
moving-coil unit, coupled acoustically to an
exponential horn. All of these have very fine
frequency characteristics, with honors at this
writing in favor of the Jensen. The Jensen is
made in California and is now generally available,
we understand. We have seen curves, above re- •
proach, which show the Jensen to have a quite
flat response curve from about 60 to 6000 cycles.
With a large baffle-board, such as obtained by
inserting the loud speaker in the walls of a home,
the lower limit of response can be pushed down
to about 35 cycles. A six-foot square baffle about
one and a half inch thick, is however, very satis-
factory.
If this Jensen unit, for example, could be made
10 TU more efficient, that is to say, deliver the
same output with one-tenth the input, the result
would be distinctly worth achieving. It should
not be forgotten, however, that aside from the
question of overall "audio" efficiency in this
unit, we must supply the coil with 60 mils, at
100 volts — 6 watts of power.
The Magnavox, too, is a fine product, but
seems to suffer from excess filters which appear
to be necessary to prevent too much a.c. hum
from getting into it, to cut down the high-pitched
heterodyne whistles, and other noises. In other
words, a Magnavox loud speaker unit without the
removable devices now employed to make up
for our present poorly filtered a.c. receivers, or
the present unfortunate situation in the ether, is
a fine unit.
We understand from an unimpeachable au-
thority that the Stromberg-Carlson engineers
built into stock receiver models a few years ago,
audio amplifiers so good that nearly all of them
came back. Criticism arose from the fact that
these receivers seemed more noisy than sets of
other manufacturers; more static came in, and
"whistles" were more evident. It was a simple
matter at the factory to put filters in the amplifier
system, cutting down on the two ends of the
frequency spectrum. Then the receivers stayed
sold. It is a fact that many hundreds of these
receivers have been sold to Bell Laboratories
engineers and their friends. As soon as they are
received out comes the soldering iron, off comes
the filters, and out of the loud speaker come the
low and high frequencies that are so essential to
good quality.
IN THE article on the four-
eAn Error in . tube "Lab" receiver in the
Coil Dimensions April RADIO BROADCAST, spec-
ifications were given in Fig. 2
for coil dimensions. Coils Li and L2 were shown
to consist of 90 turns, No. 24 s.c.c., on a form
2.5" in diameter. The correct designation should
have been 90 turns No. 24 s.c.c. on a 2.0"
diameter form. If the reader already has a 2.5"
coil form, he may use 66 turns of No. 24 s.c.c.
wire to cover the same range.
— KEITH HENNEY.
The Listeners' Point of View
HOW TO IMPROVE BROADCASTING
IN THE January number we unburdened our
soul of some ingrowing and irate convictions
in an article, "Are Radio Programs Going in
the Wrong Direction?" They were, we said, and
the general tenor of our hymn of complaint may
be recalled by quoting: "Whatever roseate
promises radio may have seemed to have held
in the past, we are at present thoroughly con-
vinced that things have reached a sorry pass, and
that radio is standing still — smug, self-satisfied,
and unutterably banal. ... In fact standstill
is putting it mildly; the state of affairs is more
exactly a retrogression. All the money, all the
ingenuity, all the labor that is being devoted to
the designing of programs is being diligently de-
voted to efforts in the wrong direction — with the
result that radio is going to the dogs at a break-
neck speed, so rapidly, in fact, that to check it
will require no little effort."
During the four months which have elapsed
since publishing this diatribe we have had an
unusual number of communications, ranging all
the way from heartiest endorsement to bitterest
denunciation.
One commentator says: "The writer is one of
those humans who inordinately admires a
'kicker' if, and when, said kicker registers his
kick with some accuracy and a lot of eclat. That
is preparatory to a 100 per cent, endorsement of
your kick in the January RADIO BROADCAST —
'Are Radio Programs Going in the Wrong Direc-
tion?' Every word in this article is pregnant with
common sense and as true as Gospel." (Such
perspicuity! J. IV.)
Another correspondent states: "You are just
like all the rest of the tribe of critics — 'smug and
self-satisfied." What good do you expect to effect
by such destructive criticism as is contained in
your article in the January RADIO BROADCAST?
Here thousands of people throughout the coun-
try have been putting in eight hours a day for
the last five years to make radio what it is to-
day and then you come along and in an article
that couldn't have taken two hours to write,
presume to set at naught all this accomplish-
ment." (O my, O my, it sometimes takes us
twenty hours to write one of these! J. IP.)
Such was the run of lay comment. We quote
two other replies, both from members of "the
profession." These retorts were not addressed
directly to us but were forwarded to "Pioneer"
of the New York Herald-Tribune who quoted
our unkind remarks in his column. One is from
the president of two small stations and the
other from the president of the National Broad-
casting Company. Mr. Donald Flamm, president
of stations WMCA and WPCH, in a lengthy open
letter said, among other things:
"It is to answer Mr. Wallace, as well as the
radio critic through whose courtesy Mr. Wal-
lace's remarks were presented, that this is writ-
ten. 1 don't propose to speak for all the broad-
casters. 1 am simply giving my own opinion,
based upon three years of association with the
radio industry and particularly with the broad-
casting end of the business. ... I, too, have come
to the realization that radio is at a standstill
and ... it is not within the province of the radio
impresario to do very much about it. And, fur-
thermore, it is going to remain at a standstill
unless some very remarkable change occurs in
the very art of radio broadcasting itself— a
By JOHN WALLACE
change that is entirely beyond our control.
. . . Let us consider . . . the plight of the broad-
caster.
"He can appeal to his audience only through
sound — nothing else. . . . There is nothing in the
world he can add to his 'tools' with which to ac-
complish so-called showmanship. There is an-
other angle that we cannot overlook . . . the fact
that the broadcaster is constantly doing some-
thing different. In writing a play, the author
takes weeks and sometimes months . . . the stage
director continues the job and shapes and
changes the play . . . until it is finally ready for a
long, or perhaps a short, run on Broadway.
The same play is repeated performance after
performance without the slightest variation of
a line or a movement. The author's job is done,
the director's job is done, the producer's job is
done. How different is the task of the broad-
caster! Every program must be different. And
as in the case of WMCA, which goes on the air
at 9 o'clock each morning and continues broad-
casting right through the day and evening until
sometimes as late as 2 A. M., what opportunity
have we for observing these rules of 'showman-
ship'?
"After all, what is there that we can present
to the public that will display good 'showman-
ship' and 'intelligence'? Radio impresarios
have presented almost every great living artist
available. There is not a musical organization
in the country whose services have not been
utilized at some time or other. During the course
of the year we have also presented hundreds of
orchestras, numerous celebrities from all walks
of life, interesting and informative talks by
competent authorities, vaudeville programs,
short programs and long programs; in short,
we have availed ourselves of every possible form
of entertainment. We have not left a stone un-
turned in our effort to bring to our audience the
complete range of program material. Beyond
that we can do no more."
Mr. M. H. Aylesworth, president of the Na-
tional Broadcasting Company said, in part:
"I have read with considerable interest the
various criticisms of broadcasting programs
. . . which you recently quoted in your interesting
column. It has occurred to me that a short re-
sume of the talent which has been made available
through the system of the National Broadcasting
Company and associated stations by American
industries who are sponsoring national programs,
as well as those produced by the National
Broadcasting Company, and associated stations
in the last sixty days (January and December),
shows something of the vast undertaking in
arrangement and finance to make possible the
feasible reception of these speakers and artists
by the American radio public." The resume,
which is entitled "A Partial List of Outstanding
Broadcasts by the National Broadcasting Com-
pany," is given herewith:
Artists, actors, and actresses — Ernest Hutche-
son, Percy Grainger, Ohman and Arden, Irene
Scharrer, Ethel Leginska, Robert Armbruster,
Ignace Friedman, Herbert Carrick, George
Gershwin, Josef Lhevinne, Adam Carroll,
Richard Rodgers, J. Milton Del Camp, Richard
Buhlig, Benno Moiseiwitsch, and Mme. Wanda
Landowska, pianists; Mischa Weisbord, Paul
3'
Kochanski, and Arcadie Birkenholz, violinists;
Ethel Hayden, Van and Schenck, Katherine
Meisle, Editha Fleischer, Reinald Werrenrath,
Maria Kurenko, Marie Tiffany, Elsie Baker,
Arthur Hacket-Granville, William Simmons,
Mary Lewis, Armand Tokatyan, Ann Mack,
Mary Garden, Al Jolson, John Charles Thomas,
Emilio de Gorgoza, Merle Alcock, Mario Cham-
lee, Duncan Sisters, Tita Ruffo, Fanny Brice,
Claudia Muzio, Cliff Edwards, Rosa Ponselle,
Giovanni Martinelli, Ezio Pinza, Richard
Crooks, and So'phie Braslau, singers; "Chick"
Sale, Joe Cook, Dr. Rockwell, Fred and Dorothy
Stone, Leo Carilla, Weber and Fields, and
Cornelia Otis Skinner, actors.
Orchestras and orchestra leaders — Walter Dam-
rosch, conducting the New York Symphony Or-
chestra; Fritz Busch, guest conductor; Roderic
Graham, conducting G. M. Symphony Orches-
tra; Patrick Conway and band, Edwin Franko
Goldman and band, Paul Whiteman and or-
chestra, Vincent Lopez and orchestra, and Ben
Bernie and orchestra.
Authors and explorers — Robert Benchley,
Will Rogers, Irvin S. Cobb, Ford Madox Ford,
Louis Golding, Glenway Westcott, Louis Brom-
field, Commander George Dyott, Fannie Hurst,
Helen Hull, Elmer Davis, Cosmo Hamilton,
S. S. Van Dine, Dr. Ralph Sockman, John B.
Kennedy, Homer Croy, Grantland Rice, and
Bruce Barton.
ARGUMENTS FOR THE DEFENSE
IN VI EW of the foregoing we have a defense of
our January remarks, and an enlargement of
them.
To those who objected that our stand was de-
structive, our retort is: It wasn't. We claim,
constructively, that serious instrumental music
should be the backbone of radio entertainment.
We offered no constructive suggestions as to
what should make up the balance of programs,
not because we had no ideas on the subject but
simply because of lack of space. Specific ideas
along those lines follow.
As for Mr. Aylesworth's reply — sorry, but
we're going to quote again from the January
squawk: "What is the right direction for pro-
gram making to take? Program makers are too
embroiled in their business to glance at the guide-
posts, too pressed by the strenuous and unceas-
ing job of making programs to take a moment
or two off for a little rational reflection on what
their job is all about. They persist in refusing to
take account of the fact that radio is a new
medium, a unique medium and, like any other
medium, endowed with its peculiar limitations
and peculiar possibilities. Pig-headedly, they
persist in attempting to reconcile with their
duties the traditions of the drama, the opera,
the music hall, and the vaudeville stage."
In view of these remarks Mr. Aylesworth's re-
buttal is seen to contain its own refutation. All
the individuals he mentions are recruited from
"the drama, the opera, the music hall, and the
concert stage." However, we will not gloat over
Mr. Aylesworth's self-confounding; our victory
is merely a dialectic one. For the fact is that the
programs he mentions are the very best that
are at present discoverable on the air.
But it is unfortunate that this is true for such
programs represent not progress, but stand-
32
RADIO BROADCAST
MAY, 1928
still. They are good in their way, but they re-
main a makeshift, a borrowing. Multiplying
them to the w'th degree would still be doing
nothing to serve the ultimate ends of radio as
a permanent institution. Radio must develop
its own artists, actors, actresses, and orchestras.
These may also do work in the other field but
they must be first of all radio performers. What
Mr. Aylesworth lists is not radio performers
but names names, names.
Mr. Flamm, quoted above, agrees with us —
but — we do not agree with him. Our version of
the predicament was not pessimistic. His is. We
claimed that nothing was being done to get
radio out of its rut. He claims that nothing can
be done.
THE BROADCASTER CAN'T IMPROVE BROADCASTING
THERE the broadcaster — if Mr. Flamm can
be taken as representative — lays all his
cards on the table and discloses himself for what
he is — an unimaginative soul who isn't fitted to
guide his own destinies. He laments that the
broadcaster can appeal only through sound. He
should rejoice. Sound. There is his medium —
plainly and unmistakably identified. There are
half a million sounds in existence awaiting his
use of them. Obdurately he ignores them. The
conclusion toward which we have been labor-
ing should by now have made itself manifest:
the broadcaster can't improve broadcasting.
If broadcasting is to be extricated from the
rut of dull routine in which it finds itself, it is evi-
dent that the help must come from without.
Why? The reason is plain enough. The broad-
caster is first of all a business man — an impre-
sario. If he transcends that he may, in some
instances, be also an interpretative artist. But
by no stretching of the imagination can he be
regarded as a creative artist. Nor are the gents
on his staff of continuity writers likely to be
creative artists. Creative artists are rare birds
and not likely to be found among the hirelings of
a big industry. The result is that nothing is
being created for radio; without creation no
art can come into being — including radio art.
True, there are program makers who go
through some of the motions of creating. But
they haven't got the goods in them and what
finally results is merely a banal, or at best
"tricky" arrangement of a lot of old stuff.
The broadcasters, however, have no occasion
to resent this indictment of their artistry. We
wouldn't have them artists! Imagine what
would happen to the National Broadcasting
Company if a crew of long haired birds should
try to run it. It would go out of business in three
days. The broadcasters are marvels of efficiency
in their own field. They have effected the most
rapid growth that any industry has ever known.
All honor is due them. The only trouble is that
they are trying to extend their field outside of
its legitimate limits. Impresarios, well and
good; but creators — phooey!
Now the truth of the matter is that there is
an Art of Broadcasting. The only trouble is that
it hasn't been discovered yet. There have been
inklings and foreshadowings of what it is to be.
But these foreshadowinps, though they're as
obvious as the nose on your face, have been prac-
tically ignored. To mention a couple of these
harbingers, one was the Eveready Hour's
"Galapagos" and the other was that same or-
ganization's "Show Boat."
These two programs came at least nearer than
any others to demonstrating what the new radio
art form will be like. But excellent as they were
they only faintly suggest the unexplored possi-
bilities of what we hereby dub "Sound Drama."
We don't propose to write you a "Sound
Drama." In the first place that's not what
we're hired to do, and in the second place we
haven't the necessary talents to do it. But it is
within our rights and powers to prophesy what
the so far unwritten "Sound Drama" will be
like. It will be a little like the Stage Drama. It
will be a little like the Opera. It will be a little
like the Symphony. It will be a little like Liter-
ature. It will be a little like the Oratorio. And it
will be exactly like no one of these. What it will
be is the perfect synthesis of all the modes we
have mentioned. Which also means it will be
quite a chore in the making! No ordinary ham
is going to be able to take all these art forms
and weld them into a whole which will be not
merely a conglomeration but a unity, an art
form in itself. It is a task for a creative artist of
the highest ability and originality. The artist
who does it will have to be Playwright, Com-
poser, and Poet all at once — in other words
such a man as was Richard Wagner. He need not
be technically equipped in each one of these
fields of art. But his taste, at least, must direct
the efforts of collaborators to a unified end. (It
is needless to add that he must also familiarize
himse'lf with the mechanical limitations of radio
transmission and adapt his music and all else
he offers to these requirements.)
The time is now ripe for the new art to appear,
for the radio lords have brought radio up to the
point where it is susceptible of being made an
art. To their credit it must be said that radio
is miles ahead of the writing that is being done
for it. Radio technicians have done astounding
things. They have developed their apparatus
and their knowledge of transmission to the point
where they can do wonders. But there are no
wonders to be done. Most of the truck that is
on the air is an insult to the excellence of the
apparatus that transmits it.
Radio play directors have made exhaustive
researches in the realm of noises. They have
learned how properly to imitate hundreds of
noises in nature. But so far they have been un-
able to put these noises to any artistic use.
. The radio engineers and the studio staffs
have done their share. They have set the stage.
What they need now is something worth while to
put on that stage. And they ought to realize
that they can't produce it. They must call for
outside help. Their position is much like that
of an expert violin maker who has put in months
of loving craftsmanship in the making of a per-
fect instrument. This same craftsman doesn't
attempt to perform on the fiddle when it is
finished. He leaves that to the artist.
So the radio program makers must sooner or
later summon the aid of the artist. An artist is
attracted to a new medium by four different
factors: ;. The artistic possibilities of the
new medium. 2. The possibilities of reaching an
appreciative audience through that medium.
3. The permanence of the medium. And, 4. The
rewards available in that medium.
That radio has artistic possibilities we are
firmly convinced. That radio has a large and
sympathetic audience is an obvious fact. That
the medium is at present a most ephemeral one
happens also to be a fact, but one of no per-
manent importance. Now, a program is given
once and forgotten sixty minutes later. Which
is generally what it deserves. But there is no
reason why a radio creation of sufficient merit
and meaty content could not be given again
and again and find a permanent place on the rep-
ertoires of stations throughout the world.
As to the rewards available for creative radio
program designing, that brings us up against the
practical. At present there is no financial in-
ducement for any one to worry his head over the
future of radio — unless he be a paid "contin-
uity" writer, in which case he does just enough
worrying to earn his salary. Many millions of
dollars are spent in this country every year on
radio programs. It is our conjecture that of these
many millions of dollars less than a tenth of one
per cent, goes to paying for the writing of broad-
cast programs. Much of it is wasted on paying
the extravagant bills of opera singers and other
overpaid interpretative artists.
If less money were lavished on the individuals
who interpret things, and more money spent in
getting them something to interpret, matters
would be vastly improved.
As a practical suggestion of a method to start
the ball rolling, we propose the following:
Let some station or syndicate of stations post
a prize of §5000 for the best specially composed
program of sixty minutes duration submitted
in manuscript by October I, 1928. The privilege
of purchasing other compositions at more ordi-
nary rates could be reserved by the station offer-
ing the prize. Certain copyright stipulations
would also have to be arranged.
What will this winning composition be like?
We will suggest its make-up. It will be a collab-
oration between a modern composer — a Hon-
neger, say — and a writer or poet. The announcer
will introduce it with not more than two or three
minutes of explanatory foreword. He will not
intrude again. This imagined program will open,
say, with a vague rumble of distant noises. They
will steadily grow louder and presently organ-
ize themselves out of the chaos into recogniz-
able sounds. They will be the noises of nature,
perhaps the beating of surf, the noise of a street,
or the buzzing of insects. They will constitute
the setting. But these noises will be craftily
selected, manipulated, minimized, or exag-
gerated. Some may be amplified to a high degree
— as they would sound, for instance, to the keen
ears of a wild animal. They will suggest the
mood of the entire piece.
Imperceptibly they will melt into music, the
music of the symphony orchestra, which will
continue to build up the mood. Then the music
will grow quieter, a modulation will change its
key and its tempo until presently it will merge,
without any break, into the human voice. Not
your ordinary human voice, but the voice of an
artist actor which can convey the slightest
nuance of emotion. And the words will not merely
be words, but just the right words. They will
be as informative as the words in any stage
play, but at the same time they will be prose
poetry. They will further clarify the situation,
or plot, which will of necessity be an elemental
and emotional one. The speaker's words may at
any time change into song and perhaps back
again. Presently the noises will be heard again, or
the orchestra, or perhaps a chorus of voices —
observers commenting on what transpires. And
so on, all these various sound sources will be man-
ipulated and shuttled about until the comedy
or the melodrama, the tragedy or fantasy, what-
ever it is, has come to a close.
In thus briefly setting down our ideas of the
possible trend of such a Sound Drama, we have
perhaps made the thing seem simply curious and
"tricky." Perhaps we have made it seem
"highbrow." If it is properly composed and ex-
ecuted it will be none of these. It will be a grip-
ping emotional thing that will completely carry
us away. It will not be something vague and dis-
jointed that we will forget immediately it is
over, but something rememberable and pleas-
urable. And it will have accomplished its end,
not through visible means, nor verbal descrip-
tion, but through an appeal to that much
neglected organ of ours — the ear.
And still the broadcaster laments that he
"can appeal to his audience only through sound
— nothing else!"
"Our Readers Suggest
OUR Readers Suggest. . ." is a regular feature
of RADIO BROADCAST, made up of contri-
butions from our readers dealing with their experi-
ences in the use of radio apparatus. Little "kinks,"
the result of experience, which five improved oper-
ation, will be described here. Regular space rates will
be paid for contributions accepted, and these should
be addressed to "Our Readers Suggest Editor,"
RADIO BROADCAST, Garden City, New York.
— THE EDITOR
Remote Volume Control
THE operation of a receiver by remote
control is an interesting possibility, and
one that has intrigued many engineering
minds. The mechanical and electrical complica-
tions of existing systems are such, however, as
to preclude their general use. It is, nevertheless,
a relatively simple matter to control the volume
of a receiver from your easy chair, which, though
only partially solving the problem, is really a
great convenience. The radio fan is, I think,
inherently a lazy individual. Writing from per-
sonal experience I may say that there is nothing
more annoying than finding it necessary to
rise from a comfortable chair or sofa to tone
down or bring up volume on a receiver that a
few minutes before was apparently correctly ad-
justed.
Fans indisposed to labor have undoubtedly
noted that the volume of a receiver is anything
but constant. An original adjustment made
when the broadcaster was using the soft pedal,
proves entirely off on a fortissimo passage. Also,
in congested radio districts, the intensity of
signals, I have found, varies considerably with
the number of receivers tuned to the same pro-
gram in the immediate neighborhood. This is not
due to an absorption effect upon the field
strength, but rather to a parallel wave trap
effect. Regardless of the reason, the condition
exists and can be made more tolerable by provid-
ing a means of volume control from wherever
the indolent listener may be reclining.
The writer uses a variable zero to five-thou-
sand ohm resistor connected between the
antenna and ground posts of the receiver by
means of a long flexible telephone cord. This is
employed as an auxiliary volume control to the
adjustment provided on the receiver itself. The
original volume control is set for a degree of
vqlume quite a bit in excess of comfortable
listening, and is toned down by the external
control.
I have found that practically any variable
resistor, covering a range of from five to at least
five-hundred ohms, is satisfactory for the pur-
pose described. It is apparently immaterial
whether or not the resistor is inductive.
JAMES MONTAGUE,
Newark, New Jersey.
STAFF COMMENT
CLECTRAD, Clarostat, Yaxley and others are
*-* manufacturing remote volume controls of
the type described by our contributor. Their use
in the antenna circuit, where, of course, signal
A NEW CLAROSTAT
It is the remote vo'ume control type. Elec-
trad Yaxley and others have similar controls
intensity is reduced before the signal is impressed
on the audio-frequency circuits, precludes the
possibility of overloading, with resulting dis-
tortion.
Devices of this nature can be made to serve a
utilitarian purpose other than Mr. Montague's
commendable moral support to laziness. Such a
volume control installed near the telephone is a
logical arrangement of genuine utility, and will
be greatly appreciated by persons who have
endeavored to converse over the 'phone in com-
petition with the radio.
Improving Your B Device
CEVERAL articles have appeared in "Our
^ Readers Suggest" department on the im-
provement of socket power devices. These
articles have considered, singly, the stabilizing
possibility of the glow tube, the use of additional
resistors to obtain desired plate potentials, and
the use of C biasing resistors. It is the purpose of
this article to describe a simple arrangement
which takes care in one unit of these various
desirable possibilities.
The starting point in improving the existing
B device is in the rectifier tube. In this connec-
tion it is necessary first to clarify a misunder-
standing which has gained ground of late,
namely, that a rectifier tube, when renewed,
must be replaced bv one of identically the same
type.
With virtually any good Raytheon B socket
power outfit heretofore provided with the Ray-
theon B type rectifier, an increase in voltage out-
put may be obtained by substituting the present
Raytheon type BH tube for the old B type. The
voltage, providing it was adequate for the re-
quirements of the output tube used before this
substitution, now is of sufficient value to take
care of the grid biasing requirements of the
power tube as well as its plate supply demands.
Other improvements for B devices have taken
the form of better voltage regulation at the
output end. Reliable potentiometer resistances,
together with a voltage regulator tube, will
maintain fixed voltages across two or more
terminals.
The photographs on page 34 present an
adapter which may be connected to many of the
better quality B power units so as to incorporate
the advantages of a potentiometer resistance net-
work and a regulator tube, while increased
voltage output is obtained for use as grid bias
by replacing the B type with the BH type Ray-
theon, as mentioned above. It will be noted from
Fig. 2 that the adapter comprises a tapped po-
tentiometer resistance, two bypass condensers, a
socket for the R (regulator) tube, and a special
current-limiting resistor for use in the third
element circuit of the regulator tube. These few
parts, along with the necessary binding posts,
may be mounted in almos,t any desirable manner.
Fig. I shows a typical B unit circuit, with the
original resistors supplying the potential re-
quirements of last year's receivers. Fig. 21 shows
a'wiring diagram of the additional unit described
by the author. Point "A" is connected to point
"A" in Fig. I and point "B" to point "B" in
Fig. I. The center choke tap runs through the
Raytheon
OBtMax.
OBtlst.A.F<
oc-
FIG.
FIG. 2
33
34
oooo-ohm resistor to the metallic base of the
regulator tube from "X" i'n Fig. 2! to "X" in
Fig. i.
The following table shows the value of the
resistors designated in Fig. 2:
RI looo ohms, 5 watts
R-2 2000 ohms, 5 watts
R3 50000 ohms, 2 watts
R< 20000 ohms, 2 watts
Rs 9000 ohms, 5 watts
R6 2000 ohms, (double potentiometer, such
the Amsco "duostat")
as
The constructor should find no difficulty in
following the layout of parts by reference to the
photographs.
D. E. REPLOOLE,
Cambridge, Massachusetts.
STAFF COMMENT
THE arrangement shown in Fig. 2 may be
used with practically any socket power
device. As was pointed out in previous articles
of this nature in "Our Readers Suggest" Depart-
ment, however, the C bias arrangement should
be employed only with a socket power unit
capable of delivering a total voltage output
under load equalling the sum of the maximum
plate and grid voltage required. The grid bias
feature may be eliminated by the omission of €2
and R6 and by the connection of the bottom of
R4 to the regulator tube and to "B" on the
regular B device. This connection is indicated in
dotted lines, the heavy line being, of course,
left out
Plate Detection
THE advantages of using a C battery for bias
in the detector circuit may be retained
without the use of an extra battery by a simple
change in the wiring of any circuit. In the
writer's case a resistance-coupled audio amplifier
is used for the first stage. The detector grid
condenser and leak are no longer used, and are
"shorted" out of the circuit.
Connect the detector rheostat in the A minus
filament line and connect the grid return as
shown in Fig. 3, which arrangement utilizes the
negative bias obtained by the drop across the
filament rheostat. A definite value of resistance
in the detector plate circuit will be found to
work best with each value of C bias. In this
case a one-megohm leak was found to be right
when ninety volts was used with a 2OI-A type
tube.
This arrangement was found to be practically
as sensitive as the usual circuit having a grid
leak and condenser, and at the same time had
Detector
Ist.A.F.
RADIO BROADCAST
This adapter, des-
cribedbyMr. Replogle,
modernises the old B
supply device. A glow
tube is used
the selectivity and tone qualities gained by
employing plate detection.
KARL V. NYQUIST,
Stromsbing, Nebraska.
STAFF COMMENT
p\ETECTING on the lower bend of the
'--' plate-current grid potential characteristic
curve, like most justifiable variations from an
average procedure, is characterized both by ad-
vantages and disadvantages. The possibility
of distortion due to overloading of the detector
circuit is reduced in the so-called plate method of
MAY, 1928
speaker can handle without distortion. The
correct adjustment can be easily made with the
aid of such simple apparatus as is generally
found in the radio equipped home.
A no-volt lamp of indiscriminate wattage,
a house current plug, and a looo-ohm resistor are
required to make the adjustment. This apparatus
is placed in series with no volts a. c. and the
loud speaker. The set screw on the loud speaker
collar is loosened and the circuit shown in Fig. 4
is closed. A I2o-cycle hum will be distinctly
heard in the loud speaker. The screws holding
the frame should be loosened slightly and the
actuating mechanism moved from side to side
and up and down until the sound is at a mini-
mum. With the set screw loosened the loud
speaker will rattle freely at this adjustment.
The current is turned off and the set screw is
tightened down upon the pin.
HARRY WIRTH,
New York City.
Selectivity with A. C. Tubes
LJAVING had occasion to alter a half dozen
* or so battery receivers for a. c. operation,
with both the R. C. A. and Arcturus types of
tube, I have noticed that the selectivity of the
battery receiver has been, in every case, notice-
ably superior to that of the rewired job. In the
course of my experiments, however, I found
that the selectivity of the a. c. set could be im-
proved until it was quite on a par with the
original 201 -A job, by
increasing the negative
bias on the r. f. tubes.
WALTER BENNETT,
New York City.
STAFF COMMENT
w
FIG. 3
A useful circuit for plate detection
AN UNDER VIEW OF THE DEVICE
DESCRIBED BY MR. REPLOGLE
detection. The sensitivity of the detecting circuit
is, however, generally lessened. In the case under
consideration, the loss in signal strength is prob-
ably negligible due to the fact that the relatively
low plate potential is secured by increasing the
resistance in the plate circuit of the detector
tube to approximately ten times the value em-
ployed in the grid current detecting system.
Increasing the value of the external plate resis-
tor in a resistance-coupled amplifier, while still
maintaining the applied plate voltage at an
optimum value for detection, increases the input
to the amplifier, which in this instance, partially
compensates the loss in detecting efficiency.
Adjusting Cone Loud Speakers
FOR THE proper adjustment of a cone loud
speaker, it is essential that the pin be
exactly centered in the collar at the apex. It
often happens that in the rough handling of
transportation the movement of the loud
speaker is shifted slightly from dead center with
the result that there is a strong tension on the
pin. This limits the amount of power the loud
ITH coils de-
signed for tubes
having the characteris-
tics of the 20 1 -A type
tube, the substitution
of alternating-current
tubes of a lower input
impedance will neces-
sarily result in the loss
of selectivity, generally
accompanied with an
increase in sensitivity.
These effects can be
compensated, as sug-
gested by Mr. Bennett,
by increasing the grid bias applied to the radio-
frequency tubes. It will be found that, at the
point at which the selectivity is equal to that of
the d. c. set, the sensitivity will also have been
readjusted to the same degree characterizing the
original battery receiver.
-AAAAA/V
1000Q
FIG. 4
A simple arrangement for the adjusting of cone
loud speakers. Unless properly adjusted, the
cone loud speaker will not give its maximum
undistorted volume
r)RODUCTS of radio manufacturers whether
± new or old are always interesting to our
readers. These pages, which will be a regular feature
of RADIO BROADCAST from this issue on will ex-
plain and illustrate certain products which have
been selected for publication because of their special
interest to our readers. This information is pre-
pared by the Technical Staff and is in a form which
we believe will be most useful. We have, wherever
possible, suggested special uses for the device men-
tioned. It is of course not possible to include all
the information about [each device which is avail-
able. Each description bears a serial number
and if you desire additional information direct
from the manufacturer concerned, please address a
letter to the Service Department, RADIO BROAD-
CAST, Garden City, New York, referring to the
serial numbers of the devices which interest you
and we shall see that your request is promptly
handled. — THE EDITOR.
A Complete A. C. Adapter Unit
X2I
Device: Marathon A. C. Harness equipment.
Consists of a cable conductor, a transformer, sup-
plying the correct voltage for Marathon tubes,
type AC 608, and a volume control. The Mara-
thon a. c. tube is of the heater type and is rated
at 6 volts and I ampere. Manufactured by the
Northern Manufacturing Company. Price:$}o.oo
(5 or 6-tube kit); seven and eight-tube units
available.
Application: In order to make the conversion of
a d. c. set to a. c. operation a simple matter using
Marathon tubes, this company is supplying the
accessory apparatus (transformer, cable, and
volume control) required. It should be under-
stood that this apparatus is made especially for
use with Marathon tubes; the transformer volt-
age is incorrect for other types of a. c. tubes.
The Marathon a. c. tube is equipped with two
New Apparatus
Complete A. C. Push-Pull Amplifier
X22
Device: Samson Power Audio Amplifier, Types
PAM-i6 and PAM-iy for use with radio re-
ceivers or phonograph pick-ups. Both types are
exactly the same except that the type PAM-iy
is equipped to supply 40 milliamperes at 120
volts to the field winding of a Magnavox, or
similar dynamic type loud speaker. The amplifier
is a two-stage transformer-coupled unit and
consists of an input transformer followed by a
THE MARATHON A. C. KIT
SAMSON PHONOGRAPH OR RADIO
AMPLIFIER
type 227 a. c. tube which in turn feeds into the
primary of a push-pull transformer. Two 210
type tubes are used in the push-pull stage. The
filaments of the 210 type tubes are operated on
a. c. and plate power for them is obtained from
a rectifier-filter system using a type 281 tube. As
indicated in the circuit diagram
one of the input leads is shielded.
This lead connects the input of
the amplifier to the output of
the detector in the radio re-
ceiver (or output of a phono-
graph pickup if one is used).
Electrically the device has been
arranged to conform with the
underwriters' specifications, all
the wiring being entirely en-
closed. The terminals of the
audio transformers project
down through the base of the
transformers into the sub-base,
and are therefore unexposed.
YAXLEY S POWER CONTROL
Manufactured by the SAMSON ELECTRIC MAN-
UFACTURING COMPANY. Price: $125.00.
Application: This amplifier can be connected to
the output of the detector tube in a radio re-
ceiver, being used therefore instead of the ampli-
fier in the set, or it may be used in conjunction
with a phonograph pick-up to reproduce phono-
graph records. At a recent R. M. A. meeting,
Mr. Cotton of the Samson Company demon-
strated the amplifier to two of the staff of RADIO
BROADCAST Laboratory and the reproduction
from phonograph records was excellent. There
was absolutely no hum audible in the Western
Electric 540 AW cone used. The unit is beauti-
fully finished and is very well arranged mechan-
ically and electrically. Complete data, blue
prints, etc., are available from the Samson
Company.
HOW TO USE THE YAXLEY POWER
CONTROL
extra terminals on the side of the
tube base and the filament trans-
former terminals need merely be
connected to these convenient termi-
nals using the harness supplied for
the purpose in this kit, and the
tubes plugged into the regular
sockets in the receiver. No adapters
are required. This is a distinct ad-
vantage when space is limited
for these tubes, when installed, will
project no higher than the stor-
age battery type tubes used
formerly in the set. When 226 and
227 type tubes are used with the
necessary adapters the overall
. height of the tube and adapter
is greater than that of a storage
battery tube and this fact will,
in some a. c. conversion jobs, give
some difficulty and necessitate re-
arrangement of some apparatus.
Shield Symphonic
CIRCUIT OF SAMSON AMPLIFIER
35
At Last — Automatic
Power Control
Device: Yaxley Full Automatic
Power Control. For the automatic
control of the power units used with
a radio receiver. Manufactured by
YAXLEY MANUFACTURING COMPANY.
Price: $7.50.
Application: This device, designed
automatically to control a receiver
installation operated from a B supply
and a trickle-charger storage battery
combination, functions (a) to turn
on the trickle charger and turn off
the B power unit when the set is
turned off, (b) turn off the trickle
charger and turn on the B power
unit when the set is turned on and,
(c) cut out the trickle charger when
the battery is fully charged. All of
36
RADIO BROADCAST
MAY, 1928
this is accomplished automatically by merely
turning the filament switch on the receiver off
and on. It is evident from the description above
that the functioning of this device differs from
that of an ordinary power control device in that
a relay in this unit is adjusted to cut out the
trickle charger when the battery is fully charged
so that there is no possibility of overcharging the
battery. The device will function with sets having
any number of tubes.
TOBE S INTERFERENCE FILTER
Heavy-Duty Interference Filter
X24
Device: Interference Filter No. 2. Consists of a
combination of filter choke coils and filter con-
densers, all assembled in a single case. Manu-
factured by the TOBE DEUTSCHMANN COMPANY.
Price: $15.00.
Application: This filter is designed for use in con-
junction with small motors and other devices
which are acting as sources of radio interference.
This filter may be used with motors rated up to
5 horsepower; for smaller motors, interference
filter No. I may be used. The filter is connected,
in series with the power line, close to the piece of
apparatus producing the interference. The Tobe
Deutschmann Company will supply any special
filter that may be necessary for unusual cases.
GENERAL RADIO PUSH-PULL AMPLIFIER
A. C. or D. C. Push-Putt Amplifier
Complete
X25
Device: Push-pull Power Amplifier Type 441.
The filament wiring is arranged so that the
filaments may be lighted from either a. c. or d. c.
The input impedance of this amplifier is 30 hen-
ries and the turns ratio of the input transformer
to the entire secondary is 4.5. The output trans-
former has a step-down ratio in voltage of 3.5
to I, to adapt the tube to the loud speaker im-
pedance. This gives a good ratio for 1 12 and
226 type tubes. If 171 type tubes are used it will
be better to connect the loud speaker between
one plate terminal and the B Plus terminal of
the output transformer. Completely assembled.
Manufactured by the GENERAL RADIO COM-
PANY. Price: $20.00.
Application: For use as a last stage amplifier in
conjunction with any standard receiver. Any
type of tube may be used in the amplifier, the
choice depending on the amount of voltage
available for driving the unit and upon the
amount of power output that is desired. This
push-pull amplifier might be used with 1 12 or 120
type tubes where moderate amounts of power are
desired and with 171 type tubes when greater
power is required. An amplifier of this type, in
use in RADIO BROADCAST Laboratory for some
time, has been giving very satisfactory results.
1/olume Control Unit
\26
Device: Table Type Clarostat. Consists of a
Clarostat variable resistance, mounted in a
small metal case, and supplied with extension
cords so that it may easily be connected between
the receiver and the loud speaker. Manufactured
by the AMERICAN MECHANICAL LABORATORIES.
Price: $2.50.
Application: A convenient accessory, readily at-
tached to any radio receiver, to control the
volume of signal from the loud speaker. And as
the advertisements say, it will control the volume
from a "whisper to a roar."
Although the device is primarily intended for
use as a volume control in the loud speaker cir-
cuit, there is no reason why it can't be put to any
of the other uses for which a Clarostat is suited,
such as controlling oscillations in the r. f. ampli-
fier, by connecting it in series with the B+ lead
to the radio frequency tubes. This device might
also be used as a volume control when con-
nected in parallel across the antenna and ground
of a receiving set installation.
Filament Transformer for A. C.
Tubes
X27
Device: A. C. Filament Lighting Transformer
Model T-i. Supplies following voltages:
I i volts — Capacity for seven type 226 tubes
25 volts — Capacity for four type 227 tubes
5 volts — Capacity for two type 1 12 or 171 tubes
The transformer is arranged with a flexible
lead to be plugged into one of three possible
jacks which permit the transformer to be
operated on line voltage from 80 to 125 volts.
Condensers and center-topped resistors neces-
sary for a. c. tubes contained in transformer
case. Manufacturer: HAROLD J. POWER, INC.
Price: $10.00.
Application: May be used to supply filament
current to a. c. tubes in a radio receiver. The
flexible lead by which different line voltages can
be compensated is an excellent feature for a. c.
tubes, especially the 227 heater type, which have a
very short life if supplied with excessive filament
voltage. Wiring diagrams of various standard
receivers revised for a. c. operation may be ob-
tained by writing the manufacturers of this
device.
Drum Dial and Adjustable Gang
Condenser
X28
Device: Gang Condenser and Drum Dial. The
apparatus contains the following features:
I. All of the condensers are mounted on a
single shaft and the condensers may be ad-
justed to any desired spacing between them
by merely loosening two set screws and slid-
PRECISE DIAL AND GANG CONDENSER
ing the condenser along the shaft to the de-
sired position.
2. Each condenser is equipped with an ad-
justment for slightly altering its capacity, so
that accurate tuning of each circuit in a
single-control set can be accomplished. The
photograph illustrates such an adjustment
being made, a procedure which is only neces-
sary when the set is placed in operation for
the first time.
3. The spacing between the condenser
plates is quite large so that the capacity of
the condenser will not be affected to any
considerable extent by variation in the thick-
ness of the plates.
4. Any number of condensers may be used
in the assembly. Each condenser has a capacity
of 0.00035 mfd. The drum dial is equipped for
a dial light and reads from o. to 100, the scale
being also approximately calibrated in wave-
lengths. Manufactured by the PRECISE
MANUFACTURING COMPANY. Price: (drum
dial assembly, $5.00; variable condensers,
0.00035 mfd., $6.00). Application: May
be used in constructing a single-control re-
Loud Speaker
X29
Device: Rola Table Type Loud Speaker, Model
20. Finished in hand-rubbed walnut, nj inches
high, i if inches wide and 6f inches deep. Fre-
quency range, according to the manufacturers,
is approximately 70 to 5000 cycles. The loud
speaker is equipped with a filter to suppress the
higher frequencies. The armature of the unit is
laminated, evidently to obtain higher efficiency.
Manufactured by the ROLA COMPANY. Price:
$35.00.
Application: This loud speaker may, of course,
be used with any standard radio receiver. The
manufacturers recommend the speaker espe-
cially for use with a. c. sets, because of its "tend-
ency to suppress and minimize the residual hum
characteristic of most a. c. sets."
NEW ROLA CONE
C4 C2 R8 R3
B+Amp. | B+135V Bt45V
IshA.F.
225V.
An A.C* Screen-Grid Receiver
ATERNATING-current operation of
screen-grid tubes has been in the minds
of many experimenters, judging from the
amount of correspondence received by RADIO
BROADCAST, and by the number of visitors to the
Laboratory who have broached this subject.
The receiver described here is the first that has
come into the Laboratory which shows how this
may be accomplished. After all the speculation
regarding the possibilities of a. c. operation of
this new tube, the trick of how to do it seems to
be no trick at all; all one needs is a source of
a. c. voltage of the proper value — 3.3. volts.
The receiver, originally designed for d. c.
operation, was described in the March RADIO
BROADCAST. It covers, with plug-in coils,
all frequencies between 100 and 10,000 kc., and
consists simply of a stage of radio-frequency
amplification using the screen grid-tube, a re-
generative detector, and two stages of audio-
frequency amplification, transformer-coupled.
All tubes in the present adaptation of this re-
ceiver operate from a. c., the voltage for the
screen-grid tube being obtained by connecting in
series the 1.5- and the 2.5-volt windings of a
standard filament transformer, and then drop-
ping the resultant 4 volts to the proper value,
3.3, by means of a 4-ohm resistance. The output
tube is a II2-A and the detector and first audio
amplifier are heater type c-32y or uv-22y tubes.
In the proper places in the circuit are bias re-
sistances so that not even C batteries are neces-
sary for the receiver's operation.
In the Laboratory the use of a. c. on the screen-
grid tube's filament contributed no a. c. hum to
the output from the loud speaker. When listening
with a pair of phones across the output, the hum
which is audible is no greater than that of any
two-stage audio amplifier and detector operating
entirely from a. c.
The difference in circuit between the original
d. c. receiver and the present one can be deter-
mined by reference to the accompanying dia-
grams, Figs. I and 2. Aside from the a. c. wiring,
and the addition of C bias resistors in their
proper places, another change is that the grid
leak is placed across the grid condenser instead
of from grid to plus filament. This is because the
heater type of tube has no filament proper, and
all grid and plate returns are connected to the
fifth or cathode post of the tube.
Reference to the diagram of the a. c. model,
Fig. 2, shows the following resistances which are
not in the d. c. set: Ri, 1500 ohms, to furnish C
bias for the screen-grid tube; R2, 64 ohms, center-
tapped, across the filament of this tube, the
center point connecting to ground through the
bias resistance; RI; Rs, 4 ohms, to drop the output
voltage of the transformer to 3.3 volts for the
filament of the screen-grid tube; R<, 1500 ohms,
in the grid return lead of the first audio tube to
supply C bias to this tube; RS, 2000 ohms, to
furnish C bias to the last tube; and R6, another
64-0(101 center-tapped resistance for the last
tube, the center connecting through the bias
resistance to ground. There are also two o. i-mfd.
condensers across the center-tapped and bias
resistances on the screen-grid tube to act as radio-
frequency bypasses, and there is a 5OO,ooo-ohm
potentiometer across the secondary of the first
audio transformer to act as a volume control. A
i-mfd. condenser across the C bias resistor of the
final tube is optional. Its inclusion will provide
better bass note reproduction. Naturally. UY
sockets must be used in place of standard sockets,
for the two heater type tubes now used in the
detector and first audio stages. Otherwise the
present receiver is exactly like the one described
in March. It covers the same frequency ranges,
= Ground
Dial Lights
FIG. I
A schematic diagram of the four-tube receiver as originally designed for d.c. operation
37
38
RADIO BROADCAST
MAY, 1928
uses the same parts, is laid out
on the pane! and baseboard
similarly, and its operation
differs not at all.
As stated before, to get 3.3
volts for the first tube's fila-
ment it is necessary to con-
nect in series the 2.5-volt and
the i.5-volt windings of the
standard filament trans-
former. If these windings are
not connected together prop-
erly, the screen-grid tube will
not light. No harm can be
done, however, by such a con-
nection, and, therefore, the
builder can easily determine
which connection is proper.
The voltage on the fila-
ment of the screen-grid tube
is not critical as to hum; the
variation in voltages occurring
in practice, due to line fluctuations etc., are not
great enough to cause hum.
While the arrangement used .or t.ie operation
of the 222 tube in the four-tube set has not been
tried with two or three r. f. stages yet, there ap-
pears no reason why it should not function satis-
factorily, and the application of a. c. operation
to two- and three-stage screen-grid r. f. amplifiers
should prove a most fertile field of experiment.
The parts used for constructing the four-tube
a. c. screen-grid receiver are listed below. While
the parts specified are recommended, the experi-
menter may substitute other makes of parts
electrically equivalent with safety:
LI — S-M 1 1 1 A Antenna Coil $ 2.50
Lj— S-M 1 1486 R. F. Coil 2.50
Two S-M 515 Universal Interchange-
able Coil Sockets 2.00
Li— Two S-M 275 R. F. Chokes i .80
T — Two S-M 240 Audio Transformers 12.00
Ci — Two S-M 320 0.0003 5-Mfd. Vari-
able Condensers 6.50
Q — S-M 342 0.00007 5-Mfd. Midget
Condenser 1 .50
Ca — Sangamo o.oooi 5-Mfd. Condenser
with Leak Clips .50
Ct — Two Fast i-Mfd. Condensers .... 1.80
C6 — Two Sprague o.i-Mfd. Bypass
Condensers i .70
Ri, R4 — Yaxley ijoo-Ohm Grid Resis-
tors i .00
R2, Re— Two Frost FT64 Balancing
Resistors 1 .00
R3 — Carter 4-Ohm Resistor .25
THE CONTROLS ARE GROUPED CLOSELY TOGETHER ON THE FRONT PANEL
R6 — Yaxley 20oo-Ohm Grid Resistor. . . .50
RT — Durham 5-Megohm Grid Leak. ... .25
Rs — Carter 5OO,ooo-Ohm Volume Con-
trol Potentiometer 2.00
Thirteen Fahnestock Connection Clips .65
Two S-M 511 Tube Sockets 1 .00
Two S-M 512 Tube Sockets 1.50
Two S-M 805 Vernier Drum Dials. . . . 6.00
7x17x3" Wood Baseboard, with Hard-
ware 1.50
i Van Doom 7x18" Decorated Metal
Panel 3.00
AND THE FOLLOWING ACCESSORIES
ux-112-A (cx-312-A) Power Tube
ux-222 (cx-322) Screened Grid Tube
Two uv-227 (c-j27) Heater Tubes
Cone Loud Speaker
Filament-Lighting Transformer with ij-, 2j-
and 5-Volt Secondaries, such as the S-M 247
Illustrated.
Three 45-Volt Heavy-Duty B Batteries, or
Any Standard Socket Power Unit Capable of
Accurate Voltage Adjustment.
The coils listed above are suitable to cover the
broadcasting frequencies. Other coils from the
same manufacturer make the receiver truly
universal insofar as wavelength range is con-
cerned.
To hook this set up, it is simply necessary to
connect the B batteries (or the socket power
supply), loud speaker, antenna and ground, to
the clips marked in the illustration, and to insert
the tubes. The filament transformer must be
f 0.000075 cnfd.
CX-312-A
connected to its appropriate clips by means of
carefully twisted wires. Preferably, it should be
situated a foot or so from the audio transformers
in the receiver.
The receiver operates exactly as any other set
of its type, the two station selector dials serving
to tune-in the different stations in the broad-
cast band of 200 to 550 meters, the midget re-
generation condenser controlling sensitivity
(regenerative amplification) and the volume
knob controlling loud speaker volume. No
"On-Off" switch has been provided in the set
for it is assumed that the socket-power unit or
filament transformer used will be provided with
a switch either in the instrument itself, or in the
connecting cord, or if in neither, the set may
easily be turned on or off at the lamp socket to
which the power unit supply cord is attached.
Using the standard 1 1 i-A and i I4-SG coils the
set tunes from 200 to 550 meters, while by
dropping the r. f. stage and connecting the
antenna to point 3 of the detector coil socket
through a small o.oooo25-mfd. midget condenser
the set will cover the shorter wavelength ranges
from 30 to 75 meters with 1 14-C coil, or 70 to
210 meters with a 114-6 coil. Waves above 550
meters may be received with a 1 1 i-D and 1 14-0
coils (500 to 1500 meters) or a 1 1 i-E and i I4-E
coil (1400 to 3000 meters). Although there
are no American broadcasting stations operating
above 550 meters there is great sport for those
who know the code on these lower frequency
bands. Ships at sea,
compass stations, air-
mail stations, time sig-
nals, and navy vessels
— all have wavelengths
covered by this receiver.
It will be necessary to
shunt the regeneration
condenser with a fixed
capacity of o.oooi-mfd.
to get good oscillation
control when the D and
E range coils are used.
1 VoltS
5V. B»A.F.
A.C.
FIG. 2
Circuit diagram of the a.c. screen grid receiver
£
0.00015,mfd.
' 3
"Time Amplifier
Q O O Q
fr326 CX- 326 CX- 326 C-327
FIG. I
Switching provides for the use of this circuit either as a super-heterodyne or as a single-circuit receiver
By Dana Adams
€
WE receiver described in this article has
several unique points of interest which
distinguish it from the commonplace. In
the first case, it is a.c. operated, a feature which
is becoming more and more popular. The most
interesting feature of the receiver, however, is
the fact that, by the mere flip of a switch, the
degree of selectivity and sensitivity of the sys-
tem may be augmented or decreased, depending
upon the requirements of the operator and his
geographical location with respect to the station
he wishes to hear. The circuit, in its most sensi-
tive form, is a super-heterodyne employing a
three-stage intermediate-frequency amplifier.
The switching, which controls the selectivity and
sensitivity, provides for three circuit arrange-
ments as follows:
ist Position: The receiver is converted into a
single-circuit receiver with one tuning control
and one volume control, the output of the de-
tector tube inputting directly to the audio
amplifier.
2nd Position: Same as ist Position with the
exception that a series condenser in the antenna
circuit is switched in by means of a Yaxley No.
10 antenna switch, thus adding a further tuning
control, but at the same time improving sensi-
tivity.
3rd Position: The complete super-heterodyne
receiver is thrown into operation, a third main
tuning control being added. The antenna tuning
condenser need not necessarily be switched into
circuit in this case.
The switch used for switching from single-circuit
receiver to super-heterodyne receiver is a Yaxley
No. 6} triple-pole switch. In Fig. I (the complete
circuit diagram up to the output of a single-
stage audio amplifier), various connections to
this switch are indicated by number but are not
grouped. The numbers for the switch terminals
are determined by counting from right to left
from a rear view of the switch.
Fig. I shows a coil and the condenser in series
with the antenna. Variation of this condenser
tunes the antenna to any desired frequency
in the same manner that the grid circuit of a tube
is tuned, with a consequent increase in signal
strength. At the same time, the strength of sig-
nals flowing in the antenna circuit at other than
the resonant frequency is reduced, following
the law of all series-tuned circuits. Laboratory
measurements show this gain at the resonant
frequency to be equal to that of one radio-
frequency stage. Coupling to the detector cir-
cuit is obtained through a small variable coil,
Li, which is a part of the Samson No. 3 1 coupler
(which comprises Lj, La, and L^). This coupling
coil, particularly when the antenna tuning is
used, is generally set very near the minimum
coupling point, with a consequent increase in
selectivity.
Having made the antenna circuit and the
coupling method as efficient as possible we turn
next to the first detector. This tube is regenera-
tive with the sensitive grid leak and condenser
method of detection and at this point the circuit
departs from the ordinary. The Yaxley No. 63
triple-pole switch is used here to cut out the os-
cillator and intermediate stages of the receiver,
at the same time transferring the first detector
plate lead from the intermediate amplifier in-
put to that of the audio amplifier. The result is
a highly efficient regenerative receiver with an
audio amplifier. The middle dial may be used
alone in tuning-in the local programs with the
antenna coupling acting as a volume control.
If additional efficiency is required, a flip of the
antenna switch makes the antenna tuning feature
immediately available.
A change of position of the three-pole switch
returns the detector plate to its normal connec-
tion in the super-heterodyne circuit, at the same
time lighting the oscillator and intermediate-
amplifier tubes, which gives us a two- or three-
dial super-heterodyne receiver. Instead of the
ordinary coupling coil method of introducing
the heterodyne frequency to the detector grid
circuit this is done by placing the oscillator coil
itself in inductive relation to the detector coil.
This eliminates the losses of signal strength
frequently caused by a tightly coupled coil
which is, in most cases, at ground potential.
The oscillator circuit is thus made entirely in-
dependent of the receiver except for its power
supply. The oscillator circuit is the familiar
modified Hartley circuit, grounded rotor plates
preventing any hand-capacity while tuning.
The beat note set up by the oscillator and first
A FRONT VIEW OF THE COMPLETE RECEIVER
39
40
RADIO BROADCAST
MAY, 1928
detector is impressed on the first intermediate'
frequency amplifier tube grid. The reader will
no doubt recognize the intermediate amplifier
as the well-known Silver-Marshall "Jeweller's
Time-Signal Amplifier" unit. The high ampli-
fication, the sharp cut off of its accurately tuned
air-core transformers, and the consistently ex-
cellent results obtained with a considerable
number of these units, are the reasons for its
selection for this receiver.
After the second detector, the audio compo-
nent of the signal is amplified by one stage of
audio amplification. A choke coil together with
the bypass condenser included in the amplifier,
combine in bypassing the radio-frequency com-
ponent of the signal to ground, thereby keeping
it out of the audio amplifier. The output of this
stage is fed to the second audio stage, which has
been omitted in the circuit diagram.
To combine the various ideas described above
in a receiver employing battery-operated tubes
is an easy matter. Fig. 2 shows such an arrange-
ment. True electric operation, however, is con-
venient and obtained in simplest, cheapest, and
least troublesome form with the tubes lighted
from an alternating-current source of supply.
Tube life when a.c. tubes are used is an impor-
tant consideration. The writer's experience in-
dicates that excessive filament voltage is the
cause of complaints of short life of the a. c.
tubes. An almost total lack of measuring instru-
ments is responsible for this condition which
time and an increase in knowledge will undoubt-
edly correct. As all tubes in this receiver are
worked at a point well under the rated voltage,
uniform and highly satisfactory results are to
be expected, the voltage adjustments being ex-
tremely easy to make.
GENERAL CONSIDERATIONS
HTHE omission of a number of details from the
^ review of the receiver, while enabling the
reader to obtain a clearer idea of the main fea-
tures, has no doubt set up a number of ques-
tions. The numbers for the switch terminals
are deterrnined by counting from right to left
from a rear view, as explained previously. The
first detector and oscillator circuits may be
easily traced with this information at hand.
These tubes in these two circuits are of the ca-
thode type in order that the beat note, tre-
mendously amplified in the intermediate stages,
will be. absolutely free from hum. The CX-J26
(ux-226) type tube is used in the three inter-
mediate stages, the 2o-ohm potentiometer, Ra,
across the filament circuit, providing a mid-tap
No, 8
NO. 3
for the grid returns. The looo-ohm potentiom-
eter, R2, biases the grids of these tubes to pre-
vent oscillation and hum, the usual method of
running the grids positive being impossible
where alternating current is employed. The
method of securing the bias voltage will be recog-
nized as that used in biasing the last audio
stage in the modern power amplifier. A 50,000-
ohm variable resistor, R4, is shunted across the
primary of the audio transformer in order to
provide an additional means of reducing the vol-
ume when the super-heterodyne is employed.
The remaining resistor, the 3Ooo-ohm poten-
tiometer, Ri, provides a common bias voltage
for the second detector and first audio stages.
The adapter which is necessary in order that
the cathode type tube may be employed in the
standard socket in the "Time-Signal Amplifier"
is omitted from the diagram for the sake of sim-
plicity. It is referred to in the list of parts. A
detailed account of this device will be found later,
in the wiring instructions. The various colored
leads, ten in number, noted in the diagram, are
provided in a single Jones ten-wire cable. This
enables the user to disconnect the power from
the receiver in a second or so. A Silver-Marshall
filament transformer is used to supply the two
filament voltages for the a.c. tubes and the volt-
age for the dial lights. Three of the cable wires
provide B voltage to the receiver while a fourth
connects the plate of the first audio tube to the
primary of the second transformer.
\A7 ITH a grasp of the main facts and an idea
* * of the principles employed, the construc-
tion of this receiver becomes an extremely simple
matter. The first step is that of assembly. All
of the apparatus, with the exception of the
"Time Amplifier," is put in the positions noted
in Fig. 3. The pointers listed below have been
gathered from the experiences of a number of
builders, and if followed carefully, will insure
perfect results.
After mounting the panels and dials the first
point to be noted in the assembly is the method
of mounting the condensers. The slotted bars
provided with the dials are removed and a one-
inch machine screw is slipped into the slot in the
dial frame. The three collars or bushings fur-
nished with each dial are slipped over the screws.
The condensers are then held in the position
shown in the photograph and the screws are
threaded into the holes provided in the conden-
ser frames. An extremely solid mounting is the
result. The tube sockets, audio transformer,
"Time Amplifier"
0.002 mfd
o o c56
Dial Lights
90V. 6V.A-C.orDC. B- Gnd. A- 45V -4>5 C
FIG. 2
Circuit arrangement for battery operation
switches, bypass condenser, choke-coil, the
jo.ooo-ohm resistor on the panel, and the an-
tenna coil require no special description. The
remaining resistors are mounted on the resis-
tor strip which is raised two inches above the
baseboard by brackets, in the following order:
In No. I position place the jooo-ohm poten-
tiometer; No. 2, the looo-ohm potentiometer;
No. 3, the 2o-ohm potentiometer; No. 4, the
5O,ooo-ohm resistor.
The double rotor coupler (consisting of L2,
La, U) used in the first detector circuit to secure
variable antenna coupling and regeneration
requires altering before mounting. All but
eight turns are removed from the antenna coup-
ling rotor, L>, which is controlled by the lower
of the two knobs. The oscillator coil also re-
quires alteration before mounting. Eight turns
are removed from the outside end of the large
or grid winding of the coil, Ls. This is done so
that the detector and oscillator control settings
will match although tuned 112 kc. apart. The
wire removed from this coil should be added to
the plate coil, L«, at the bottom, insuring suffi-
cient feedback to cause oscillation. This coil is
then mounted three eighths of an inch from the
coupler, as shown in the photograph, to insure
proper coupling.
The wiring of the first detector, audio stage,
and oscillator circuits is the next step. A twisted
pair from the pink and blue terminals of the
cable to each pair of dial light terminals eli-
minates these from further calculation. From
the yellow and black terminals another twisted
pair is connected to the contacts of the mid-tap
resistor mounted on the filament posts of the
audio tube socket. From this point the pair is
continued to the detector socket and from there
one wire goes to the oscillator tube socket
while the other connects to Contact No. 5 on
the triple-pole switch. A wire from No. 4 con-
tact on the switch to the remaining filament
post completes the wiring of the heater circuits.
The remaining wiring to these three tubes may
be easily traced from the diagram.
All filament, cathode, and B battery wiring
should be formed along the main cable, as shown
in the photograph, wherever possible. The leads
from the plate of the detector to the switch, from
the antenna coil to the coupling coil, and other
leads at a high potential from a radio-frequency
standpoint, should be formed in a secondary
cable close to the panel. Avoid right-angle
bends on grid and plate connections; the shorter
they are, the better. In wiring the oscillator cir-
cuit be sure that the grid and plate connect to
the outside ends of their respective coils, or the
tube will not oscillate. Pin-jacks may be moun-
ted at the ends of the resistor strip so that a
phonograph pick-up or one of the "home-
broadcasting" microphones may be employed.
One pin-jack should be connected to B minus
and the other to the plate terminal of the audio
transformer.
The drilling instructions for the resistor strip
are shown in Fig. 3. Only two of the three con-
nections on the looo- and 3Ooo-ohm potentiom-
eters are employed as their function is that of a
variable resistor rather than a bridge resistance
in this circuit.
The "Time-Signal Amplifier" should be put
in position next. The filament wiring should be
twisted together and the remaining leads run-
ning the length of the receiver should be formed
into the main cable. The B minus, plus 45 volt,
and plus go volt connections should be picked
up at the nearest point in the wiring of the
other tubes and connected to the proper posts
on the amplifier.
The adapter for the second detector tube,
referred to previously, is provided with a pair
MAY, 1928
A FLEXIBLE A.C. SUPER-HETERODYNE
41
Cable Block-, Resistor Strip
Time Amplifier
o o o
Osc.
Cond.
Sec.
Cond.
LAYOUT OF PARTS
50,000 W
Ant
Cond.
o o o
Q 0 0
£
> -^-« -£
> ^
~CM
Y
^i/'
<-- 3"—
„
* 415-"-,.
•*- - -- 4^5 *"
<-- 3- ->
FRONT PANEL LAYOUT
<
'"ft*
*'
Jc
-I*"-
•M^*
RESISTOR STRIP
FIG. 3
of filament leads, the pins that normally would
supply filament power being dummies. These
leads are twisted together and connected to the
filament terminals of the oscillator tube socket,
the detector then turning on or off with the rest
of the intermediate tubes. The grid and plate
make the normal connections to the circuit
through the adapter pins while the cathode is
brought to the pin normally used for negative
filament. The wire connecting to the correspond-
ing post on the socket inside the can should be
unsoldered and a new wire run out of the shield
from this post and connected to the cathode post
of the audio amplifier tube socket. The removal
of this connection, which is merely a connection
to the shield, does not disturb the circuit in any
way. The bypass shown across the B and P
terminals of the amplifier is most important, as
well as the radio-frequency choke in the output
lead of this amplifier.
The receiver is now ready for test. To do this
properly the power unit that is to be used must
be at hand. A few suggestions anent this unit
will undoubtedly assist those who are not fa-
miliar with this adjunct to quality reception.
The combination of a full-wave rectifier, a good
filter circuit, and a voltage regulator tube pro-
vide the best possible B voltage supply. As the
unit is also used to secure C bias, its freedom
from ripple is important. Naturally a push-pull
cx-3io (ux-2io) stage represents the last word
for a tremendous amount of undistorted output
although a cx-37i a (ux-iyi) stage will be found
sufficient in the average home.
The first step in testing is to throw the
switch to the single-circuit receiver position. A
minute should elapse before the receiver starts
functioning. The jooo-ohm resistor should be
set at the halfway position. Failure to operate
may be readily traced in this simple two-tube
set. Hum audible over a foot from the loud
speaker indicates either oscillation, in which
case the tickler should be adjusted, or an open
circuit. A check of the B voltage at the plate
and a test for open grid circuits is sure to locate
the trouble. The panel resistor should be turned
to the left to obtain
greatest volume. After
tuning up and down the
dial a few times the an-
tenna tuning should be
tested by opening the
switch. Its effect will be
noticed more readily on
the weaker stations. The
dial setting may be
matched within a few
divisions of the detector
dial by putting a few
turns of wire in series
with the antenna. This
will be necessary only
where a short antenna is
employed. Up to 150 feet
may be used without
fear of broad tuning, as-
suring a stronger signal
from distant stations.
TheosciHater is tested
by tuning-in a station
in the middle or lower
portion of the wave band
and temporarily short-
circuiting contacts Nos.
4 and 5 of the switch.
After the tube has
warmed up the dial
should be rotated. A
loud heterodyne squeal
on the incoming signal
indicates the proper
functioning of the oscillator. A check up on
the connection and the continuity of the grid
and plate circuits will readily correct any trouble.
The third step in the testing is that of the
intermediate amplifier. The looo-ohm resistor
should be set at a quarter turn from the zero
bias point, the 1 5-ohm potentiometer at the mid-
point, and the B resistor slightly below the full-
voltage position. A turn of the switch and a few
moments wait should see the super-heterodyne
in operation. A rapid succession of "birdies"
when the oscillator is tuned indicates oscillation
in the intermediate stages. This is the only
trouble that will be encountered rf the wiring
has been done in the correct manner. It is
readily corrected by reducing the filament volt-
age. An o. 5-ohm rheostat, which should be located
at the filament transformer end of the cable,
is the remedy. A slight readjustment of the
bias and B-voltage resistor will also be of assis-
tance. It should be borne in mind that the ampli-
fier should be adjusted
so that maximum am-
plification is obtained
at all times. The input
is controlled by the an-
tenna coupling while
the resistor across the
transformer primary
may be used as an
auxiliary means of re-
ducing the tremendous
volume that may be
obtained, to a reason-
able level. While the
rheostat takes care of
the voltage applied to
the cx-326 (ux-226)
tubes in excellent fash-
ion, care should be
taken that the cathode
tubes are not run at
an excessive voltage.
If the receiver is to
be operated from an A
battery and is toderive
its plate voltage from either batteries or power-
supply unit, various changes must be made. Three
S-M No. 51 1 sockets will be required in place of the
three No. 512 ones indicated in the list of parts.
Two Carter I R-6 6-ohm rheostats, R> and RIO, are
also necessary. A Carter M-4OO-S potentiometer-
filament control switch, Rg, is also wired in the
circuit. The list of parts for the a.c. receiver:
LIST OF PARTS
Ci, Q, Cs — Samson No. 65 o.oooj-Mfd. Con-
densers 122.50
Li — Samson No. 71 Antenna Coil 2.75
L«, Li, Li — Samson No. 31 Coupler 7.50
Li. Le— Samson No. 41 Oscillator Coil 2. 85
Three Marco No. 421 Illuminated Con-
trols 10.50
S-M No. 440 Time Amplifier (Includes
Three Intermediate Stages and 2nd
Detector)
T — S-M No. 220 Audio Transformer
LT— S-M No. 276 Choke Coil
Three S-M No. 512 Tube Sockets
Sw — Yaxley No. 10 Antenna Switch
One Yaxley No. 63 Triple-Pole Switch
Ri-^-Carter MW-3ooo jooo-Ohm Poten-
tiometer
Rz-^-Carter MW-iooo lOOO-Ohm Poten-
tiometer
Ra — Carter MP-2O 20-Ohm Potentiometer
RI, Rt, — Carter Type L 5O,ooo-Ohm " Hi-
Ohm"
Carter Cathode Tube Adapter
Re — Durham 2-Megohm Leak
RT — Frost FT-64 Mid-Tap Resistor
Cf— -Carter o.oooi5-Mfd. Grid Condenser,
with Clips
C6 — Carter o.oo2-Mfd. Condenser
C6 — Carter No. 210 i-Mfd. Bypass Con-
denser
Jones No. BM 410 Ten-Wire Cable
Cortlandt Panel 7" x 24" x Ta6" Drilled and
Engraved
Resistor Mounting Strip ij" x -j\" x -fa"
Drilled
Baseboard 12" x 23" x J", Plywood Pre-
ferred
Two Rolls of "Braidite" Wire, Two
Colors
One Fahnestock Clip and Assorted
Screws
Total
35.00
8.00
i.oo
2.25
.50
1. 60
1.25
1.25
•75
4.00
I.IO
.50
.50
.40
.50
1.25
3-25
7.50
i"
50
•75
.60
70
$118.25
The following additional equipment is partly
necessary to operate the receiver. A choice in
several instances may be made by the construc-
tor.
Four c-327 Tubes £2400
Three cx-326 Tubes 9.00
TI — SM 325 Filament Transformer 8.00
One S-M 660-210 Power Pack or — 83.50
One S-M 660 171 Power Pack 66.50
One Fritts Cabinet 7" x 24" x 12" 23.50
HOW THE PARTS ARE LAID OUT
The coil units to the left comprise Lj, La,
LA, Lt, and Le, while Li is to the right
AS THE BROADCASTER SEES IT
Design and Operation of Broadcasting Stations
ig. Frequency Runs
THE various elements of the circuits used
in broadcasting exhibit effects which de-
pend, among other factors, on the fre-
quency of the potentials applied to them. A
line, for example, tends to attenuate voice cur-
rents of high frequency more than currents of
lower frequency, because of the shunting ef-
fect of the distributed capacity, which varies
with the frequency. More specifically, we may
say that every piece of apparatus has a definite
transmission characteristic with frequency,
which it is necessary to know if organizations of
apparatus are to be brought about for given
objects, for example, impartial or "flat" repro-
duction of sounds of different pitches. Such a
curve of amplitude against frequency is secured
by means of a frequency run. In broadcasting
the most common frequency runs are made
within the audio band, say between 50 and
10,000 cycles per second, and typical circuit
amplitude of 5-per cent, is allowable, but the
proportion must not be greater. The power out-
put of the oscillator should be reasonably con-
stant over the range of frequency, and it is not
difficult to design an oscillator which will meet
this requirement within 5 per cent, output volt-
age variation over a 50 to io,ooo-cycle band. The
oscillator may be one of several types. One form
consists of audio tuned circuits, generally em-
ploying fixed condensers and obtaining the fre-
quency variation by means of taps on an iron
core coil of suitable inductance. The inductance
and capacitance together tune to the audio fre-
quency directly. Another type of audio oscillator
utilizes the heterodyne principle. Two radio-
frequency oscillators have their outputs com-
bined, rectified, and, if necessary, amplified at
audio frequency. Generally one of the compon-
ent oscillators has its frequency fixed; the other
radio frequency is varied, and the beats may be
made to cover the whole audible range. Pre-
cautions must be taken to avoid too much fre-
Repe
Co
o
o
o
C2>
Equalizer
Audio
Amplifier
I
Volume
Indicator
atmg
I
500
ohms
FIG. I
elements which require this sort of investigation
are telephone lines and the audio circuits of
transmitters. Representative methods of making
such tests will be briefly described in this article.
Fig. i is a diagram showing how a frequency
run may be made on a wire line, using an audio
oscillator at the transmitting end and vacuum-
tube voltmeters for the indicating instruments.
The audio oscillator in all such work must ful-
fil several requirements. It must cover the
frequency range over which the circuit is to
be equalized. For ordinary line work, by present
standards, this would be from 100 to 5000 cycles,
hence the oscillator of Fig. i will have to more
than cover this band — a 50 to6ooo-cycle oscillator
would be suitable. The output must be substan-
tially free from harmonics. Obviously since the
instrument is to be used in determining fre-
quency characteristics one must be able to secure
oscillations of any frequency in the range with-
out the admixture of other frequencies. If, for
example, the behavior of the line is to be studied
at 200 cycles, the harmonics (400, 600, 800 . . .
cycles) must be suppressed. Usually a harmonic
quency drift, owing to varying voltages, and there
is also a tendency for the two radio oscillators
to pull into synchronism at the lower beat fre-
quencies. Some information on the construction
of audio beat oscillators for laboratory testing
is contained in several 1927 papers in the Pro-
ceedings of the Institute of Radio Engineers
(Wolff and Ringel: "Loud Speaker Testing
Methods," May, 1927; Dickey: "Notes on the
Testing of Audio-Frequency Amplifiers," Aug-
ust, 1927; Diamond and Webb: "Testing of
Audio-Frequency Transformers," September,
1927). In general, broadcasters who lack labora-
tory training in measurements will do better if
they buy such instruments as audio oscillators.
Such apparatus is sold by the General Radio
Company, Graybar Electric Company, and
other concerns. Oscillators covering a range of
from 10 to 50,000 cycles, or higher, with defi-
nitely known output characteristics, are obtain-
able. One form covers from 1 5 to 9000 cycles,
continuously variable through a single control;
the price is a little more than $200.
Returning now to Fig. I, we note that the re-
ceiving instrument is a "volume indicator" of
the vacuum-tube type. The circuits of a typical
form are shown in Fig. 2. The action will not be
taken up in great detail, as a previous article in
this series ("Volume Indicators," RADIO BROAD-
CAST, May, 1927) dealt with the general theory.
In the form shown the negative grid bias is ad-
justed until the d.c. galvanometer in the plate
circuit of the tube reads 5 scale divisions out of
a total of 60 full-scale. Then the tap on the
secondary of the input transformer is set to give
peak readings, with modulation, of, say, 30 scale
divisions. The level of the circuit across which
the instrument is bridged may then be read on a
scale attached to the transformer tap switch.
High levels, obviously, correspond to settings
in which only a small portion of the total trans-
former voltage is utilized, whereas when the tele-
phonic level is low, more of the winding must be
included by means of the tap switch in order to
get the requisite galvanometer swing. Obviously
the readings of such an instrument are the re-
sultant of many factors, such as the wave form
of the alternating currents under measure-
ment, the ballistic characteristics of the gal-
vanometer, the size of the galvanometer shunt,
the smoothing characteristics of the inductance-
capacitance filter in the plate circuit, the type
of vacuum tube employed, and other details,
but it is possible to design such level indicators
to read in telephonic transmission units with
sufficient accuracy for the usual purposes of
broadcast transmission or measurement. The
prototype is the Western Electric 518-6 type,
which, in its lowest range, from minus m to
plus 10 TU, is constructed as shown in Fig.
2, but extends the range of measurable levels to
as high as plus 40 TU by the addition of a poten-
tiometer arrangement across the secondary of
the input transformer.
Obviously a level indicator must always be a
bridging instrument, a circuit element, that is,
with a relatively high input impedance, intended
for connection across circuits of low impedance
without drawing enough energy from the low-
impedance circuit to affect conditions therein.
MAY, 1928
AS THE BROADCASTER SEES IT
43
The volume indicator described above has an
input impedance of about 12,000 ohms and it
must be used across a 500- or 6oo-ohm circuit if
its calibration is to hold. It is so connected in'
the set-up for a line frequency run shown in
Fig. I. The output of the oscillator is of 500
ohms impedance. This feeds a IO-TU artificial
line which presents an impedance of 500 ohms
in each direction. The usual repeating coil is
inserted ahead of the line. The line is assumed to
have an impedance of about 500 ohms also. At
the other end of the line there is an equalizer
(See article on "Types of Equalizers," RADIO
BROADCAST, June, 1026) followed by a two-
stage amplifier, with an output impedance of
500 ohms. This amplifier must be terminated
with a resistance of this magnitude, therefore,
before the level readings of a volume indicator
bridged across it will be valid.
Since the equalizer is at the far end of the
line, the latter will not present a strictly con-
stant impedance at the transmitting end, and
this would affect the output of the oscillator if
instrument were connected directly to the line.
The artificial line acts as a buffer, in that it pro-
vides a more constant impedance for the oscilla-
tor to feed into; in some cases the artificial line
network also permits measurement at more
convenient levels without excessive input to the
telephone line.
The procedure for a frequency run is obvious
from this point on. The oscillator is set at various
frequencies, the outgoing level checked with the
volume indicator across it, and similar readings
taken at the receiving end. A curve of received
level against frequency may thus be secured for
a given setting of the equalizer. If the equalizer
is omitted, and the transmitted level remains
constant, such a curve will show the line attenu-
ation characteristic, which is a curve descending
with frequency. The object of the equalizer being
to correct this loss of the higher frequencies, a
number of frequency runs may be taken, until
a horizontal curve of received level is secured.
The line is then equalized. Communication be-
tween the two terminals may be maintained over
the line by telephone or telegraph in the inter-
vals between readings, or over a separate pair.
Of course before an attempt is made to take a
frequency characteristic of a line, or to set the
equalizer for a flat characteristic, the usual d.c.
wire chief's tests are made for defects like open
circuits or grounds. Nothing in the way of audio-
frequency testing can be accomplished until such
faults have been eliminated.
HOW NOT TO DO IT
CIG. 3 shows a method of taking line fre-
quency runs which is illegitimate. I have
seen it used, and so mention it here with the
caution that results so secured will usually be
misleading. The oscillator, with the volume in-
dicator bridged across it, is connected across a
500-ohm resistance and the level is read. The
output of the oscillator is then switched to a
line, the equalizer being at the other end. In
this way a frequency run is made and the line
is thought to be equalized. Actually, as the
impedance of the line varies with the frequency,
the output of the oscillator will also vary with
frequency and the result of the experiment will
merely be to show how the oscillator behaves
with a variable impedance connected across its
terminals.
Sometimes it is convenient to send out tone
on a line using the regular broadcast amplifier
set-up. For example, in chain operation it is a
sound precaution to transmit tones at a number
of important frequencies before a program.
The network stations take level readings at the
various frequencies transmitted, which may be
Audio
Oscillator
Volume
Indicator
FIG. 3
100, 1000, and 5000 cycles, and telegraph them
back as a check on the condition of the lines.
Any irregularity will show up in these readings
and necessary changes in routing of circuits,
adjustment of terminal apparatus, etc., may be
made before the program begins. Fig. 4, from the
input of the three-stage amplifier, is the usual set-
up for broadcasting. The input to the first am-
plifier would normally be a microphone. For the
microphone there has been substituted the audio
oscillator, a repeating coil, and a variable at-
tenuation network, which can be adjusted to any
loss up to 30 TU. By means of this pad the
level of the outgoing tone may be made the
same as that normally used during broadcast-
ing—usually around zero level (12 milliwatts on
peaks, or about 5 milliamperes into a 5OO-ohm
circuit).
In the December, 1924, issue of the Proceedings
of the Institute of Radio Engineers, Mr. Julius
Weinberger showed a means of taking the audio-
frequency characteristic of the modulation sys-
tem of a radio station. The diagram is repro-
duced, with some slight modifications, in Fig.
5 herewith. The audio oscillator in this case
Audio
Oscillator
Repeating
Coil
Variable
Pad
3 -Stage
Audio
Amplifier
10 Tu
Pad
2 -Stage
Audio
Amplifier
10 Tu
Pad
amplitude compared with the transmission of
the mean speech frequency (1000 cycles), or in
TU, the horizontal axis representing frequency.
The thermo-galvanometers in such a set-up
as that shown in Fig. 5 must necessarily have
the right full-scale reading for the circuits under
measurement. The required capacity can readily
be calculated, since the output of the oscillator,
the amplification of the audio system, and there-
fore the alternating voltage developed by the
modulators, will all be approximately known.
Where there is any doubt a large instrument is
first used, until one of the right sensitiveness
and current-carrying capacity is found. As the
output measurements are made across the full
plate voltage the engineer who works on this
end must take the usual precautions against
accidental contact with the high-tension por-
tions of the equipment.
RADIO FOLK You SHOULD KNOW
4. E. B. Pilhbury
[F THERE is a communication man in the
'United States it is Edward Butler Pillsbury,
the Vice President and General Manager, as
well as a Director, of the Radio Real Estate
Corporation of America, the holding company
for the realty properties of the R. C. A. Mr.
Pillsbury has spent his entire career in teleg-
raphy, starting as a messenger, working ten years
as a Western Union operator, followed by many
years in the service of the Postal Telegraph-
Cable Company, first as Chief Operator in Bos-
Repeating
Coil
FIG. 4
feeds into a 5OO-ohm resistance, matching its
normal output impedance. A thermo-galvanom-
eter in series measures the a.c. emitted by the
oscillator. A portion of the voltage across the
500-ohm resistor is fed into the line amplifier
of the station with enough added resistance on
either side to maintain the 5OO-ohm impedance.
The tone passes through the entire audio-fre-
quency system and the level is measured at the
output of the modulators. A fixed condenser of
j-mfd. capacity blocks the direct plate voltage
and allows only the audio component to affect
the measurement circuits. The lower terminal
of the condenser is connected to ground through
a resistance of the order of 20,000 ohms, which
is so high that the characteristics of the trans-
mitter will be unaffected by the addition of
the measuring circuit. A relatively small portion
of the audio voltage across the resistor is tapped
off for the thermo-galvanometer. A radio-
frequency trap is usually required to keep r.f.
out of the galvanometer circuit. The current
readings of the input and output galvanometers
will now give the transmission characteristics
of the modulation system at any frequency
within the compass of the oscillator. The curve
may be drawn with ordinates of percentage of
150 ohms
ton, then advancing to the grades of local Man-
ager in that city, Assistant Superintendent,
District Superintendent for New England, and
finally General Superintendent of the Eastern
Division of the company, with jurisdiction over
the lines and offices in thirteen states from his
headquarters in New York. This position
Mr. Pillsbury held for six years, until he re-
signed to take up radio work as General Super-
intendent of the Transoceanic Division of the
Marconi Wireless Telegraph Company of Amer-
ica, and later for the Radio Corporation. In
1922 he was elected to his present office.
While serving as an operator Mr. Pillsbury
was renowned as an expert Morse man. He was
among the first chief operators to-adopt the prac-
tice of using the Wheatstone bridge method of
locating faults on telegraph lines.
Anyone else who has seen all he has of the
communication business and of life would be
writing his memoirs. But when Mr. Pillsbury
was asked to supply information for this bio-
graphical sketch he replied plaintively. " I re-
gret to say that no interesting anecdotes or ex-
periences have come my way." Press agents
should thank God that the country is not
crowded with Edward Butler Piltsburys.
FIG. 5
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333 333333
RADIO BROADCAST ADVERTISER
47
The Thordarson Z.-Coupler,
a special audio impedance
coupler for use with screen
grid tubes; price each, S12.
Screen grid audio amplification, most
revolutionary development in audio
systems since the introduction of the
power tube, is now an established fact.
The Thordarson Z-Coupler is a special
audio coupling device designed for use
with the screen grid tube UX-222.
With the remarkable amplification
thus obtained a mere whisper from the t
detector is stepped up to a point that
'gives the power tube all it can handle
in the way of signal voltage. In fact,
one stage Z-Coupled audio has the am-
plification equivalent of two, or even
three, stages of ordinary coupling. Sig-
nals barely audible before may now i
heard at normal room volume.
In tone quality, too, the Z-Coupler is
unexcelled. Despite the high amplifi-
cation the tonal reproduction is as
nearly perfect as any audio amplifier
yet developed. Both high and low
notes come through with the same vol-
ume increase. Even at 60 cycles the
amplification is over 95% of maximum.
Regardless of the type of your receiver
you can vastly improve its perform-
ance by including this new system of
' amplification. The Z-Coupler replaces
the second audio transformer, with
very few changes in the wiring. The
screen grid tube is used in the first
audio stage. No shielding is required.
<ov Complete
information
THORDARSON ELECTRIC MFG. CO.
Huron and Kingshury Sts., Chicago, 111.
Gentlemen :
Without obligation on my part, please send
me complete information on screen grid audio
amplifiers using your new Z-Coupler. (3578-J)
Name
Street and No...-
Town
...State.
RADIO BROADCAST ADVERTISER
orit use old
orlnferiorlubes
with New ones
Use new
throughout
and enjoy
modern radio
reception at
its best
E.T. CUNNINGHAM, inc.
New York Ch i cago
San Francisco
The Radio Broadcast
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 11527, an index to all Sheets appearing up to
that time was printed. This month we print an index covering the sheets published from
August, 1927, to May, 1928, inclusive.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. I to 88, can be secured from the Circulation Department,
Doubleday, Doran & Company, Inc., Garden City, New York, for Ji.oo. Some readers
have asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any serious errors do occur, a new Laboratory Sheet with the old
number will appear
— THE EDITOR.
No. 185
RADIO BROADCAST Laboratory Information Sheet
Tube Overloading
May, 1928
EFFECT OF INCORRECT VOLTAGES
DURING recent years many familiar types of
radio tubes have played the role of "Jack of
all trades," and as a result have frequently been
placed in service under conditions never intended or
contemplated by the manufacturer.
What constitutes "overload" on a tube, re-
sulting in shortened life? It might be imagined that
the |ast tube in a receiver tuned-in on a strong local
station, and with the volume turned up beyond the
point where the music sounds clear, would fall
under this classification, but this is not the case.
This is a form of overloading, but one which only
results in distorted music, and in general the tube is
not affected at all. A severe overload permanently
affecting the tube occurs, however, when the manu-
facturer s specifications as regards filament, plate,
and grid voltages are disregarded and higher volt-
ages are used.
One of the popular tube types affords a good illus-
tration of this condition. The voltages recommended
for type 201 -A tubes area filament voltage of 5.0
volts, and plate voltages of 90 to 135 volts, with the
grid bias specified as -4.5 and -9.0 volts respec-
tively. If the grid bias of 4.5 volts recommended at
90 volts is omitted it is equivalent to adding about
35 volts to the plate voltage, or in other words, is
equivalent to operation of the tube at 125 volts
with -4.5 volts bias. The overload is, of course,
correspondingly more severe if the plate voltage is
raised. This is clearly shown in the table below:
PLATE
VOLTS
90
135
90
120
135
GRID CURRENT
VOLTS
4.5
9.0
0
0
0
MA.
2.0
2.5
6.0
9.8
12.0
EXTENT OF
OVERLOAD
Below maximum
Normal
58%
240%
380%
The 201-A type tube is capable of withstanding
some overload more successfully than other types
of tubes, but as a general rule it is always advisable
to follow the manufacturer's ratings regarding tube
voltage.
No. 186
RADIO BROADCAST Laboratory Information Sheet
The UX-250 and CX-350
May, 1928
A NEW POWER AMPLIFIER
THE ux-250 (cx-350) is the latest tube designed
for use as a power amplifier to supply large
amounts of undistorted power for the operation of
loud speakers. The large output obtainable from
this tube prevents any possibility of overloading
of the last stage of an audio amplifier.
The filament rating is 7.5 volts, 1.25 amperes.
The material used in the filament is the rugged
coated ribbon form, similar to that used in the ux-
2bO (cx-380) rectifier, the filament operating at a
dull red. The filament current may be supplied from
the 7.5-volt winding of a power transformer. The
low operating temperature and the increased size
of this type of filament results in minimum ripple
voltage or "hum."
It should be noted that, althougfi the filament
and plate voltages are the same as those for the
ux-210 (cx-310) tube, the plate current is 55 milli-
amperes at a plate voltage of 400 volts whereas un-
der similar conditions, the plate current of the ux-
210 (cx-310) is only 18 milliamperes. The grid
voltages for these two tubes, at a plate voltage of
400 volts, are respectively — 70and —31.5. the larger
voltage being necessary on the ux-250 (cx-350)
tube. Because of the higher plate current and grid
bias required by this new tube it cannot always be
used to replace the ux-210 (cx-310) tube without
changing the circuit.
Plate Voltage
Negative Grid Bias
Plate Current
Plate Resistance (a.c.)
Mutual Conductance
Voltage Amplification Factor
Max. Undistorted Power Output
Filament 7.5 Volts 1 . 25 Amperes
Max. Overall Height 6i" Diameter 2 IS"
Base: Large Standard ux (ex)
RECOMMENDED
250 300 350 400
45 54 63 70
28 35 45 55
2100 "2000 1900 1800
1800 1900 2000 2100
3.8 38 3.8 3.8
900 1500 2350 3250
MAXIMUM
450 Volts
84 Volt
55 Milliamp.
1800 Ohms
2100Micromhos
3.8
4650 Milliwatts
RADIO BROADCAST ADVERTISER
49
N
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Cle-Ra-Tone Sockets
For Standard UX Type
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toP
A new Five Prong Socket
for A. C. Detector Tubes.
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You can tell immediately into what socket each tube
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Improves the appearance of the set.
Cle-Ra-Tone Sockets are spring supported to absorb
the shocks that distort tonal qualities. The tube
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shocks and jars from slamming doors, passing traffic
and other disturbances caused by outside vibrations.
One-piece terminal to tube connection. Positive con-
tacts. Knurled nuts for binding post connections or
handy lugs for soldering.
Cle-Ra'Tone Sockets have been chosen for practically
every prominent circuit for several years.
At All Radio Jobbers and Dealers
Benjamin Electric Mfg. Co.
12O-128 So. Sangamon St., Chicago
247 W. 17th St. 448 Bryant St.
New York San Francisco r
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More
POWER
From Your Eliminator
If your Raytheon
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not hold its volt'
tage when sup-
plying one or
two 1?1 or 371
tubes, you can
probably bring
it back to full voltage by the addi'
tion of an Aerovox Condenser as
shown. Here is the circuit. The
Condenser is a 4 Mfd. type 402.
«!/>
fJtTffl
f \t/
/ i^..
f *t
The Aerovox "Research Worker" contains much use-
ful and interesting information, A postcard will
fiut your name on the mailing list.
78 WASHINGTON ST.
BROOKLYN, N. Y.
4RBORPHONE
R4DIO
AC-
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HAMMARLUND
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Soldered brass plates with tie-bars;
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Made in all standard capacities
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The "Midline" is but one of many Hammar-
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Single (in all standard capacities for long and
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RADIO BROADCAST ADVERTISER
oAdds the
: Final Touch
TABLE TYPE
Reg. U. S. Pat. Off.
CT'HE ideal control for volume and tone
J. of your loud-speaker, from soft, sooth-
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Ask your radio dealer to show you the Table
Type Clarostat and give you copy of "Radio
Etiquette". Or write us direct for interesting
data on improving your radio.
American Mechanical Laboratories
Incorporated
Specialists in Variable Resistors
285-7 N. Sixth St., Brooklyn. N, Y.
Used Exclusively
in the
COOLEY
Rayfoto Receiver
Approvedby
A. G. COOLEY
For Further Information Address
L.S.BRA.CH
MFG. COFtR
ENGINEERS AND MANUFACTURERS
NEWARK. N J u'.S. A. TORONTO. CAN.
No. 187
RADIO BROADCAST Laboratory Information Sheet
Grid Bias
May, 1928
HOW TO CALCULATE BIAS
'TMIIS Laboratory Information Sheet gives some
*• information regarding grid bias and how it
depends upon the voltage of the grid battery and
the manner in which the filament circuit of the
tube is wired.
The bias voltage on the grid of a tube is always
specified with respect to the negative end of the
filament. In drawing A of the diagram on Sheet
No. 188, the grid voltage is zero.
In drawing B, the filament resistance K has been
placed in the negative leg of the filament, and since
the drop across this resistance is 1.0 volt, the grid
bias is also —1.0 volt.
In drawing C, a 4^-volt battery has been intro-
duced in the circuit so that the grid bias is now equal
to the voltage of this battery plus the voltage drop
across the resistance R. The bias is therefore — 4J
plus - 1.0 or -5J volts.
A positive grid bias of +6.0 volts is obtained if
the resistance K is connected in the positive leg of
the filament and the grid return is connected to the
+A terminal of the battery. See sketch D. If the
grid return was connected to the other leg of the
resistance, the grid bias would be equal to the volt-
age drop in the filament or 4-5.0 volts.
A variable grid bias from —1.0 to +5.0 volts can
be obtained by means of the potentiometer P in
drawing E. With the potentiometer at the extreme
left-hand position, the bias is — 1.0 volt (due to the
voltage drop in R) and with the arm moved over
to the extreme right-hand position the bias is +5.0
volts.
From the information given in this Sheet it
should be possible to determine the grid bias with
any circuit arrangement.
No. 188
(A)
RADIO BROADCAST Laboratory Information Sheet May, 1928
Grid Bias Calculations
(B) (C) (D) (E)
Laboratory Sheet No. 187 explains these five circuit arrangements. De-
termination of the grid bias of any circuit arrangement is a simple matter
once the information contained on these sheets is mastered
No. 189
RADIO BROADCAST Laboratory Information Sheet
The A. C. "Universal" Receiver
May, 1928
PARTS REQUIRED
T ABORATORY Sheet No. 190 gives the circuit
^-* of the "Universal" receiver wired for a.c.
operation. The d.c. receiver was described in the
December, 1926, RADIO BROADCAST and the circuit
of the d.c. receiver was also given on Laboratory
Sheet No. 100, June, 1927. The a.c. circuit is pub-
lished in response to many requests from readers.
Li — Antenna coil consisting of 13 turns of No. 26
d.s.c. wire wound at one end of a 2J-inch tube.
La — Secondary coil consisting of 50 turns of No.
26 d.s.c. wire wound on the same tube as Li. The
separation between L! and L-j should be i inch.
Ls — Primary of interstage coil constructed in same
manner as Li and tapped at the exact center.
L4 — Secondary winding constructed in same man-
ner as Lj and tapped at point A, the 15th turn from
that end as L4 which is nearest to La.
Ci, Cj — Two 0.0005-mfd. variable condensers.
Cs — -Neutralizing condenser, variable, 0.000015
mfd.
C( — Regeneration condenser, 0.00005 mfd.
Ls — R.F. choke coil, made by winding 400 turns
of No. 28 wire on J" dowel.
Ti, T! — Two audio-frequency transformers.
R! — Fixed resistance, 1000 ohms.
R2, Rs, Ri — Center-tapped resistances for a.c.
tubes.
R» — Fiied resistance, 2000 ohms.
Re — Grid leak, 2 megohms.
CB, Cs — Bypass condensers, 1-mfd.
Ci — Grid condenser, 0.00025-mfd.
Cs — Output condenser, 200 volts, 4-mfd.
LG — Output choke, 60 henries.
VT,, VTa — 226 type a.c. tubes.
VT» — 227 type a.c. tube.
VT, — 171 type tube.
Three standard four-prong, sockets.
One five-prong socket.
Binding posts.
C bias for the tubes is obtained from resist-
ances Ri and Rs.
The 227 type detector tube requires about 30
seconds to heat up and begin functioning and there-
fore about this length of time must lapse between
the time the power is turned on and the set begins
to operate. The receiver must, of course, be carefully
neutralized.
RADIO BROADCAST ADVERTISER
51
190
RADIO BROADCAST Laboratory Information Sheet
May. 1928
A revised ar-
rangement of the
well-known
"Universal" cir-
cuit which pro-
vides for the use
ofa.c. tubes. It is
fully described
on Labor atorv
Sheet No. 189
To Filament Lighting
Transformer
To 6 Power Unit
No. 191 RADIO BROADCAST Laboratory Information Sheet
Index
August, 1927, to May, 1928
May, 1928
SHEET
NUMBER MONTH
<,
Glow Tubes:
Acoustics
NUMBER
166
MONTH
February
How they function
Why they are used
Grid Bias
129
173
October
March
A Battery Chargers
120
August
Calculating Its Value
187
May
Audio Amplifier:
Why It Is Used
174
March
A.C. Operated 148,149
Frequency and load characteristic 118
December
August
Hertz Antenna
Honeycomb Coils, Data on
121
130
September
October
General considerations
165
February
Inductive Reactance
139,140
November
Resistance-Coupled
131,132
October
Loud Speakers:
Transformer Ratio, Effect of
Capacity, The Unit of
179
138
April
November
Exponential Type
General Considerations
134
145
October
December
Carrier Telephony
136
October
Modulated Oscillator
164
February
Chargers, A Battery
Choke Coils, Radio-Frequency
Condenser Reactance
Constant Frequency Stations
Coupled Circuits
120
119
126,127
153
135
August
August
September
January
October
Morse Code
Oscillation Control
Output Devices
Overloading, Effect on Tube
Power Supply Devices:
Calculation of various toll-
125
150
113
185
September
December
August
May
Ear, Characteristics of the
168
February
ages
142
November
Exponential Horn, The
178
April
Care of
133
October
Fading
Filter Choke Coils
Filter Condensers
Gain, R. F. Amplifiers
160
175
182
147
January
March
April
December
Characteristics at various
voltages
Desirable Characteristics
Transformer Voltages, Ef-
fect of
146
128
180
December
September
April
No. 192 RADIO BROADCAST Laboratory Informition Sheet
Index (Continued)
August, 1927, to May, 1928
May, 1928
SHEET
NUMBER
MONTH
Radio-Frequency Choke Coils
R. F. vs. A. F. Amplification
Receivers, Testing of
Resonant Circuits
Roberts Reflex, The
Selectivity
Sensitivity
Single-Control Receiver,
Boosting Sensitivity of
SHEET
NUMBER
119
181
122
163
167
158,159
170
170
151
MONTH
August
April
September
February
February
January
March
March
December
Tubes:
Alternating-Current Types
Comparison of 112 and 171
Comparison of 112, 171, and
210
Effect of plate circuit on £rid
circuit
Parallel Operation
171
112-A
171-A
222
280 and 281
141
17.1
161,162
176
137
123,124
154
154
169
183
November
March
February
March
November
September
January
January
March
April
Solenoid Coil Data
143
November
250
186
May
Speech:
Tuning, Effect of Distributed
Articulation
Sources of Information on
177
152
April
December
Capacity on
"Universal" Receiver, A. C.
184
April
Standard Frequency Stations
Static
Super-heterodyne, The
Transmission Unit, The
153
116
117
114
January
August
August
August
Operation of
Wavelength-Frequency Con-
version
Wavemeter, A Simple
Wave Traps
189,190
156,157
172
155
May
January
March
January
145
December
115
August
Announcing Dongan
By-Pass and Filter
Type
Condensers
With the acquisition of
the business and equip-
ment of the Electrical
Specialties Mfg. Company,
Inc., Dongan now offers
the manufacturers of ra-
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q'uality and ingenuity of
design to Dongan Radio
Transformers.
Mr. C. Ringwald, an au-
thority on condenser de-
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will direct the condenser
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radio line.
Just as Dongan has pi-
oneered in transformer de-
velopment, so will the
Dongan laboratories strive
to maintain front rank in
fixed condenser design.
Thus the radio industry
is assured additional per-
manency in the approved
parts field.
Dongan will continue its
policy as an exclusive
source to set manufacturers
—another Transformer Success
To meet the increased capacity
of the new UX 250 power ampli-
fier tube, Dongan engineers have
perfected two new Output Trans-
formers. No. 1176 is Push Pull
type, _ No. 1177 a straight power
amplifier type.
A Popular A C Transformer
No. 6flZ
Thin is one of the be>t-liked A C trans-
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THIS transmitter is a small condenser which
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is coupled direct into a single stage of ampli-
fication, contained in the cast aluminum case.
The output, reduced to 200 ohms, couples
to the usual input amplifier. The complete
transmitter may be mounted on the regulation
microphone stand. It operates on 180 v. B and
6 or 12 v. A battery.
This transmitter contains no carbon, and is
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Price, complete with 20 ft. shielded cable,
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Send for our bulletins on Broadcasting
Equipment
PRESS, WEATHER, AND TIME SIGNALS
THE list below has just been released by the Navy
Department, radio service, to RADIO BROADCAST.
It includes the press, weather hydrographic, and time
signals transmitted by United States Naval Stations
throughout the world. This list supersedes that ap-
pearing on page 514 of this magazine for March, 1927.
The material in columns three and four below is of es-
pecial interest. The abbreviations employed and their
meaning follows: "i.c.w." interrupted continuous wave;
"c.w.," continuous wave; "a.c.w.," raw a.c. These trans-
missions are of vital importance to all marine and shore
station operators. Other readers who are interested in
listening to these signals should employ a simple re-
generative circuit with a long antenna. A satisfactory
receiver for this purpose was described on RADIO
BROADCAST Laboratory Information Sheet No. 19,
August 1926. Also, the article, "A Portable Long- Wave
Receiver," page 166, RADIO BROADCAST, July 1927,
describes a receiver especially designed for long-wave
reception.
TIME
(GREENWICH
Civil.)
STATION
CALL SIGN
FREQUENCY IN
KC/S AND TYPE
OF EMISSION
MATERIAL BROADCAST
0000
Brownsville, Tex.
NAY
132 i. c. w.
Weather.
0045
San Juan, P. R.
NAU
48 c.w. •
Weather (1 July to 15
November).
0100
Norfolk. Va.
Puget Sound, Wash.
NAM
NPC
122 i.c.w.
118 c.w.
Weather
Weather.
0115
Arlington, Va.
NAA
4015 i.c.w.
Aviation weather and
upper air reports.
0130
Eureka, Calif.
Norfolk, Va.
NPW
NAM
104 i.c.w.
122 i.c.w.
Weather, hydrographic.
Weather.
0200
Cavite, P. I.
Guantanamo Bay, Cuba.
San Juan, P. R.
NPO
NAW
NAU
56 c.w. & 112 i.c.w.
118 i.c.w.
106 i.c.w.
Press.
Weather (1 June to 15
November).
Weather (1 July to 15
November) .
0255 to 0300
Arlington. Va.
Annapolis, Md.
Cavite, P. I.
NAA
NSS
NPO
112 i.c.w.
690 i.c.w.
4015 i.c.w.
8030 i.c.w.
12045 i.c.w.
17.6 c.w.
56 c.w.
112 i.c.w.
Time Signals.
Time Signals.
Time Signals.
0300
Arlington, Va.
Cavite, P. I.
Key West, Fla.
Puget Sound, Wash.
NAA
NPO
NAR
NPC
36 c.w.
112 i.c.w.
56 c.w.
112 i.c.w.
102 i.c.w.
118 c.w.
Marine Weather fotlou-ed
by Navigational Warn-
ings and ice reports (in
season).
Weather, hydrographic.
Weather, hydrographic.
Hydrographic.
0305
Navy Yard, Wash. D. C.
NAA
690 voice
Weather.
0330
San Francisco, Calif.
Tutuila, Samoa
NPG
NPU
42.8 c.w.
108 i.c.w.
66 c.w.
Weather, hydrographic.
Hydrographic.
0355 to 0400
Balboa, C. Z.
Colon, C. Z.
NBA
NAX
46 c.w.
132 i.c.w.
Time Signals.
Time Signals.
0400
Arlington, Va.
Great Lakes, 111.
Puget Sound, Wash.
San Juan, P. R.
NAA
NAJ
NPC
NAU
4015 i.c.w.
132 i.c.w.
118 c.w.
48 c.w.
Weather broadcast to
Europe.
Weather, hydrographic.
Weather.
Weather.
0430
Astoria, Oreg.
San Diego, Calif.
NPE
NPL
112 i.c.w.
102 i.c.w.
Hydrographic.
Weather.
0500
Brownsville, Tex.
NAY
132 i.c.w.
Weather.
0555 to 0600
San Francisco, Calif.
NPG
42.8 c.w.
62 c.w.
108 i.c.w.
Time Signals.
0600
San Francisco, Calif.
NPG
108 i.c.w.
Weather, hydrographic.
0630
Honolulu, T. H.
NPM
54 a.c.w.
Weather, hydrographic.
0700
Annapolis, Md.
Arlington, Va.
NSS
NAA
17.6 c.w.
112 i.c.w.
Press.
Press.
0730
Tutuila, Samoa
NPU
66 c.w.
Hydrographic.
1000
Balboa, C. Z.
Balboa, C. Z.
Colon, C. Z.
San Diego, Calif.
NBA
NBA
NAX
NPL
46 c.w.
118 c.w.
132 i.c.w.
30.6 c.w.
Press and hydrographic.
Press.
Hydrographic.
Press.
1300
Puget Sound, Wash.
NPC
118 c.w.
Weather.
1315
Arlington, Va.
NAA
4015 i.c.w.
8030 i.c.w.
12045 i.c.w.
Aviation weather and
upper air reports.
1330
Norfolk, Va.
NAM
122 i.c.w.
Weather.
1355 to 1400
Cavite, P. I.
NPO
56 c.w.
112 i.c.w.
Time Signals.
1400
Cavite, P. I.
NPO
56 c.w.
112 i.c.w.
Weather, hydrographic.
1500
Arlington, Va.
NAA
112 i.c.w.
16060 i.c.w.
Marine weather followed
by ice reports (in season) .
1505
Arlington, Va.
NAA
690 voice
Weather.
RADIO BROADCAST ADVERTISER
53
PRESS, WEATHER, AND TIME SIGNALS
(Continued)
A TIME CONVERSION TABLE
TIME
(GREENWICH
CIVIL)
STATION
CALL SIGN
FREQUENCY IN
KC/S AND TYPE
OK EMISSION
MATERIAL BROADCAST
IfviO
New York, N. Y.
Charleston, S. C.
NAH
NAO
108 i.c.w.
122 i.c.w.
Weather, hydrographic.
Weathe-r, hydrographic.
1545
Philadelphia, Pa.
Great Lakes, 111.
Norfolk, Va.
NAI
NAJ
NAM
104 i.c.w.
132 i.c.w.
122 i.c.w.
Weather, hydrographic.
Weather, hydrographic.
Weather, hydrographic.
1600
Boston, Mass.
Newport, R. I.
Arlington, Va.
New Orleans, La.
San Juan, P. R.
Savannah, Ga.
NAD
NAF
NAA
NAT
NAU
NEV
102 i.c.w.
118 i.c.w.
12045 i.c.w.
106 c.w.
48 c.w.
132 i.c.w.
Weather, hydrographic.
Weather, hydrographic.
Weather broadcast to
Europe.
Weather, hvdrographic.
Weather.
Weather.
1630
Jupiter, Fla.
San Diego, Calif.
St. Augustine, Fla.
NAQ
NPL
NAP
132 i.c.w.
102 i.c.w.
128 spark
Weather.
Weather.
Weather.
1645
Pensacola, Fla.
NAS
112 i.c.w.
Weather.
1655 to 1700
Arlington, Va.
Annapolis, Md.
Great Lakes, 111.
Key West, Fla.
New Orleans, La.
San Diego, Calif.
NAA
NSS
NAJ
NAR
NAT
NPL
112 i.c.w.
690 i.c.w.
4015 i.c.w.
8030 i.c.w.
12045 i.c.w.
17.6 c.w.
132 i.c.w.
102 i.c.w.
106 c.w.
30.6 c.w.
102 i.c.w.
Time Signals.
Time Signals
Time Signals
Time Signals
Time Signals
Time Signals
1700
Arlington, Va.
Brownsville, Tex.
Eureka. Calif.
Key West, Fla.
Puget Sound, Wash.
San Francisco, Calif.
NAA
NAY
NPW
NAR
NPC
NPG
112 i.c.w.
132 i.c.w.
104 i.c.w.
102 i.c.w.
118 c.w.
42.8 c.w.
Navigational warnings.
Weather.
Weather, hydrographic.
Weather, hydrographic.
Weather, hydrographic.
Weather, hydrographic.
1755 to 1800
Balboa, C. Z.
Colon, C. Z.
NBA
NAX
46 c.w.
132 spark
Time Signals.
Time Signals.
1800
Balboa, C. Z.
NBA
46 c.w.
Hydrographic.
1830
Honolulu, T. H.
NPM
54 a. c.w.
Weather, hydrographic.
1930
Tutuila, Samoa
NPU
66 c.w.
Hydrographic.
1955 to 2000
Astoria, Oreg.
Eureka, Calif.
San Francisco, Calif.
NPE
NPW
NPG
112 i.c.w.
104 i.c.w.
42.8 c.w.
62 c.w.
108 c.w.
Time Signals.
Time Signals.
Time Signals.
2045
Arlington, Va.
NAA
690 voice
Weather.
2100
Norfolk, Va.
Puget Sound, Wash.
NAM
NPC
122 i.c.w.
118 c.w.
Weather, hydrographic.
Weather, hydrographic.
2130
Astoria, Oreg.
NPE
112 i.c.w.
Hydrographic.
2200
Boston, Mass.
Newport, R. I.
New York. N. Y.
Phila. Pa.
Annapolis, Md.
Eureka, Calif.
Great Lakes, 111.
New Orleans, La.
San Diego, Calif.
NAD
NAF
NAH
NAI
NSS
NPW
NAJ
NAT
NPL
102 i.c.w
118 i.c.w
108 i.c.w
101 i.c.w
17.6 c.w.
1O1 i.c.w
132 i.c.w
106 c.w.
102 i.c.w.
Weather, hydrographic.
Weather, hydrographic.
Weather, hvdrographic.
Weather, hydrographic.
Ice reports (in season).
Weather, hydrographic.
Hydrographic.
Weather, hvdrographic.
Weather.
2230
Honolulu, T. H.
NPM
54 a. c.w.
Weather, hvdrographic.
2300
Charleston, S. C.
Jupiter, Fla.
Pensacola, Fla.
Savannah, Ga.
NAO
NAQ
NAS
NEV
122 i.c.w.
132 a.c.w.
112 i.c.w.
132 i.c.w.
Weather, hvdrographic.
Weather.
Weather.
Weather.
2330
Tutuila, Samoa
NPU
66 c.w.
Hydrographic.
2355 to 2400
Honolulu, T. H.
NPM
26. i.c.w.
106 i.c.w.
Time signals.
/^REENWICH Mean Time was adopted
VJ by the recent International Radio Tele-
graph Convention in Washington for use in
the Convention and regulations drawn up by
it. Greenwich Civil Time is used in the Navy
for navigation and that time is employed in
naval almanacs. The conversion table below
indicates the relation between G.C.T., G.M.T..
and 75th Meridian Time. The latter is "East-
ern Standard" Time and those living in other
time belts can easily calculate the time to listen
for these transmissions in their own locality.
G.C.T.
(Hours)
0
6
12
14
18
22
24
G.M.T.
(Hours)
12
18
0
2
6
10
12
75TH MERIDIAN
7.00 p.m.
1.00p.m.
7.00 p.m.
9.00 p.m.
1.00p.m.
5.00 p.m.
7.00 p.m.
Electrify Your Set
WITH THE
MARATHON
JICK1T
SIMPLE AS A-B-C
Marathon AC Tubes
have the standard 4
prong UX bases. No
adaptors or center tap
Replace i|our old Tubes
with Marafhon A-CTubes
The Marathon harness
is universal, and can be
used in any set. The
"spades" slip over the
projections on the tube
— no thumb screws.
Connect the harness
One end of the harness
connects with the
Marathon Trans-
former. All tubss oper-
ate on one voltage — 6
volts — so there are no
in the Unfit tcrlef ^ps. Simply plug the
Ml IIIC IICJIII WCBer transformer Into the
that's all there istodo light 80cket'
YOU CAN'T MAKE IT
COMPLICATED
No need to wonder if
the Marathon AC Kit
will operate on your set
— we guarantee it. If
you have a 5, 6, 7 or 8
tube set using UX
sockets and are now
employing an **A" Bat-
tery (either dry cell or
storage) you can use
the Marathon A C Kit — perfectly.
Marathon AC Tubes are guaran-
teed for a year. If your dealer
cannot supply you use the cou-
pon below.
The Marathon AC Kit
is Complete
Nothing else to buy — everything
Is complete. For example the six
tube kit includes 6 Marathon AC Tubes — a uni-
Jobbers^— Dealers
Write or wire for our sales proposition. You can ab-
solutely guarantee the operation of the Marathon
AC Kit.
NORTHERN MFG. CO.
NEWARK, NEW JERSEY
Northern Manufacturing Co.,
376 Ogden St., Newark, N. J.
Send me complete information on the
Marathon AC Kit.
Jobber Dealer
Professional Builder 1 »,-r
(Please check your claaification)
Name
Address
RADIO BROADCAST ADVERTISER
New Aero Circuits
for Either Battery or A. C. Operation
Proper constants for A. C. operation of the Im-
proved Aero-Dyne 6 and the Aero Seven have been
studied out, and these excellent circuits are now
adaptable to either A. C. or battery operation. A. C.
blue prints are packed in foundation units. They
may also be obtained by sending asc for each direct
to the factory.
Aero Universal
Tuned Radio Frequency Kit
Especially designed for the Improved Aero-Dyne 6.
Kit consists of 4 twice-matched units. Adaptable to
20I-A, ipg, 112, and the new 240 and A. C. Tubes.
Tuning range below 200 to above 550 meters.
Code No. U-16 (for .0005 Cond.) $15.00
Code No. U-163 (for .00035 Cond.) 15.00
Aero Seven
Tuned Radio Frequency Kit
Especially designed for the Aero 7. Kit consists
of 3 twice-matched units. Coils are wound on Bake-
lite skeleton forms, assuring a 95 per cent, air dielec-
tric. Tuning range from below 200 to above 550
meters. Adaptable to aio-A, 199, 112, and the new
240 and A. C. Tubes.
Code No. U-12 (for .0005 Cond.)... ...$12.00
Code No. U-123 (for .00035 Cond.) 12.00
You ihtmld be able to get any of the above
Aero Coil* and part* from your dealer.
If he should be out of stock order
direct from the factory.
AERO PRODUCTS, INC.
1772 Wilson Ave. Dept. 109 Chicago, III.
Flexible A. C.
Superheterodyne
An aristocrat of a famous family espec-
ially designed to meet the demands of that
select circle of set builders who desire the
finest in receiver construction with cost a
secondary consideration.
Complete detailed blueprints on this
unique combination of the best radio prin-
ciples, $1.00 postpaid. All specified parts
supplied. Price list on request.
DANA ADAMS
222 East 52nd St. N. Y. City
Western Office: 6O4 Davis St., Evaiuton, III.
Radio
Convenience
Outlets
Wire your home for radio. These out-
lets fit any standard switch box. Full
instructions with each outlet.
No. 135— For Loud Speaker Sl.OO
No. 137 — For Battery Connections 2.50
No. 136 For Aerial and Ground 1.00
With Bakelite Plate*
Now furnished with a rich satin brown Bakelite
plate, with beautiful markings to harmonize, at
25 cents extra. See Illustration.
At Your Dealers
Yaxley Mfg. Company
Depl. B, 9 So. Clinton St.
Chicago. III.
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
? may obtain any of tbe booklets listed below by use-
'^- ing tbe coupon printed on page 57. Order by number only.
1. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS — A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-
TION—Circuit diagrams and discussion. ALL-AMERICAN
RADIO CORPORATION.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
it. RESISTANCE COUPLING — Resistors and their ap-
plication to audio amplification, with circuit diagrams.
UEjuR PRODUCTS COMPANY.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
1 5. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE CONDENSERS — A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their application to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
17. BAKELITE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
20. AUDIO AMPLIFICATION — A booklet containing data
on audio amplification together with hints for the construc-
tor. ALL AMERICAN RADIO CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE-
METER — Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
positions in the circuit where audio-frequency chokes may
be used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio- frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED.
51. SHORT-WAVE RECEIVER— Constructional data on a
receiver which, by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY — A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL. INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA— Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. RESISTANCE COUPLING — A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION
62. RADio-FREguFNcv AMPLIFICATION — Constructional
details of a five-tube icceiver using a special design of radio-
frequency transformer. CAMFIELD RADIO MFG. COMPANY.
63. FIVE-TUBE RECEIVER— Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
66. SUPER-HETERODYNE — Constructional details of a
seven-tube set. G. C. EVANS COMPANY.
70. IMPROVING THE AUDIO AMPLIFIER — Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used.
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM — A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY.
80. FIVE-TUBE RECEIVER — Data are given for the con-
struction of a five-tube tuned radio-frequency receiver.
Complete instructions, list of parts, circuit diagram, and
template are given. ALL-AMERICAN RADIO CORPORATION.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
82. SIX-TUBE RECEIVER— A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams,
and templates for the construction and assembly of socket
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Panel layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequency
transformers of special design. KARAS ELECTRIC COMPANY,
85. FILTER — Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A socket
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimental
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blue print and necessary
data, for building an eight-tube receiver. THE GEORGE W.
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER— Data and blue prints
are given on the construction of a short-wave transmitter,.
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES.
90. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification are
given. ALDEN MANUFACTURING COMPANY.
93. B-SOCKET POWER— A booklet giving constructional
details of a socket-power device using either the BH or 313.
type rectifier. NATIONAL COMPANY, INCORPORATED.
94 POWER AMPLIFIER — Constructional data and wiring.
diagrams of a power amplifier combined with a B-supply
unit are given. NATIONAL COMPANY, INCORPORATED.
too. A, B, AND C SOCKET-POWER SUPPLY — A booklet
giving data on the construction and operation of a socket
power supply using the new high-current rectifier tube.
THE Q. R. S. Music COMPANY.
101. USING CHOKES — A folder with circuit diagrams of
the more popular circuits showing where choke coils may
be placed to produce better results. SAMSON ELECTRIC
COMPANY.
22. A PRIMER OF ELECTRICITY — Fundamentals of
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
26. DRY CELLS FOR TRANSMITTERS — Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS— Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE — Battery life curves with general
curves on tube characteristics. BURGESS BATTERY COM-
PANY.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
32. METERS FOR RADIO — A catalogue of meters used in
radio, with diagrams. BURTON-ROGERS COMPANY.
33. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. WHY RADIO Is BETTER WITH BATTERY POWER — Ad-
vice on what dry cell battery to use; their application to
radio, with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR — Information on the care of
vacuum tubes, with notes on how and when they should be
reactivated. THE STERLING MANUFACTURING COMPANY.
69. VACUUM TUBES— A booklet giving the characteris-
tics of the various tube types with a short description of
where they may be used in the circuit. RADIO CORPORA-
TION OF AMERICA.
77. TUBES — A booklet for the beginner who is interested
in vacuum tubes. A non-technical consideration of the
various elements in the tube as well as their position in the
receiver. CLEARTRON VACUUM TUBE COMPANY.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
91. VACUUM TUBES — A booklet giving the characteristics
and uses of various types of tubes. This booklet may be
obtained in English, Spanish, or Portuguese. DEFOREST
RADIO COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS — A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new 4OO-milIiampere rectifier tube. CARTER RADIO
COMPANY.
102. RADIO POWER BULLETINS — Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
103. A. C. TUBES — The design and operating character-
istics of a new a. c. tube. Five circuit diagrams show how
to convert well-known circuits. SOVEREIGN ELECTRIC &
MANUFACTURING COMPANY.
41. BABY RADIO TRANSMITTER OF 9XH-9EK — Descrip-
tion and circuit diagrams of dry-eel! operated transmitter.
BURGESS BATTERY COMPANY.
42. ARCTIC RADIO EQUIPMENT — Description and circuit
details of short-wave receiver and transmitter used in
Arctic exploration. BURGESS BATTERY COMPANY.
58. How TO SELECT A RECEIVER — A commonsense
booklet describing what a radio set is, and what you should
expect from it. in language that any one can understand.
DAY-FAN ELECTRIC COMPANY.
67. WEATHER FOR RADIO — A very interesting booklet
on the relationship between weather and radio reception,
with maps and data on forecasting the probable results.
TAYLOR INSTRUMENT COMPANIES.
(Continued on page 55)
RADIO BROADCAST ADVERTISER
55
73. RADIO SIMPLIFIED — A non-technical booklet giving
pertinent data on various radio subjects. Of especial in-
terest to the beginner and set owner. CROSLEY RADIO COR-
PORATION.
76. RADIO INSTRUMENTS — A description of various
meters used in radio and electrical circuits together with a
short discussion of their uses. JEWELL ELECTRICAL IN-
STRUMENT COMPANY.
78. ELECTRICAL TROUBLES — A pamphlet describing
the use of electrical testing instruments in automotive work
combined with a description of the cadmium test for stor-
age batteries. Of interest to the owner of storage batteries.
BL-RTON ROGERS COMPANY.
95. RESISTANCE DATA — Successive bulletins regarding
the use of resistors in various parts of the radio circuit.
INTERNATIONAL RESISTANCE COMPANY.
96. VACUUM TUBE TESTING — A booklet giving pertinent
data on how to test vacuum tubes with special reference to
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT
COMPANY.
98. COPPER SHIELDING — A booklet giving information
on the use of shielding in radio receivers, with notes and
diagrams showing how it may be applied practically. Of
special interest to the home constructor. THE COPPER AND
BRASS RESEARCH ASSOCIATION.
99. RADIO CONVENIENCE OUTLETS — A folder giving
diagrams and specifications for installing loud speakers in
various locations at some distance from the receiving set.
YAXLEY MANUFACTURING COMPANY.
105. COILS — Excellent data on a radio- frequency coil
with constructional information on six broadcast receivers,
two short-wave receivers, and several transmitting circuits.
AERO PRODUCTS COMPANY.
106. AUDIO TRANSFORMER — Data on a high-quality
audio transformer with circuits for use. Also useful data on
detector and amplifier tubes. SANGAMO ELECTRIC COMPANY.
107. VACUUM TUBES — Data on vacuum tubes with
facts about each. KEN-RAD COMPANY.
108. VACUUM TUBES — Operating characteristics of an
a.c. tube with curves and circuit diagram for connection
in converting various receivers to a.c. operation with a
four-prong a.c. tube. ARCTURUS RADIO COMPANY..
109. RECEIVER CONSTRUCTION— Constructional data on
a six-tube receiver using restricted field coils. BODINE
ELECTRIC COMPANY.
i io. RECEIVER CONSTRUCTION — Circuit diagram and
constructional information for building a five-tube set
using restricted field coils. BODINE ELECTRIC COMPANY.
in. STORAGE BATTERY CARE— Booklet describing the
care and operation of the storage battery in the home.
MARKO STORAGE BATTERY COMPANY.
112. HEAVY-DUTY RESISTORS — Circuit calculations and
data on receiving and transmitting resistances for a variety
of uses, diagrams for popular power supply circuits, d.c. resis-
tors for battery charging use. WARD LEONARD ELECTRIC
COMPANY.
1 13. CONE LOUD SPEAKERS — Technical and practical in-
formation on electro-dynamic and permanent magnet type
cone loud speakers. THE MAGNAVOX COMPANY-
114. TUBE ADAPTERS — Concise information concerning
simplified methods of including various power tubes in
existing receivers. ALDEN MANUFACTURING COMPANY.
115. WHAT SET SHALL I BUILD?— Descriptive matter,
with illustrations, of fourteen popular receivers for the home
constructor. HERBERT H. FROST, INCORPORATED.
104. OSCILLATION CONTROL WITH THE "PHASATROL" —
Circuit diagrams, details for connection in circuit, and
specific operating suggestions for using the "Phasatrol"
as a balancing device to control oscillation. ELECTRAD,
INCORPORATED.
1 16. USING A B POWER UNIT — A comprehensiv: book-
let detailing the use of a B power unit. Tables of voltages —
both B and C — are shown. There is a chapter on trouble-
shooting. MODERN ELECTRIC MFG. Co.
117. BEST RESULTS FROM RADIO TUBES — The chapters
are entitled: "RadioTubes," "Power Tubes," "Super De-
tector Tubes," "A. C. Tubes," "Rectifier Tubes," and
"Installation." GOLD SEAL ELECTRICAL Co.
118. RADIO INSTRUMENTS. CIRCULAR "J" — A descriptive
manual on the use of measuring instruments for .-very radio
circuit requirement. A complete listing of models for trans-
mitters, receivers, set servicing, and power unit control.
WESTON ELECTRICAL INSTRUMENT CORPORATION.
119. THE NEW IXJFTIN WHITE CIRCUIT — A twenty-four
page booklet explaining the principles and application of
this popular circuit. CONSOLIDATED RADIO CORPORATION.
120. THE RESEARCH WORKER— A monthly bulletin of in-
terest to the home constructor. A typical feature article
describes the construction of a special audio amplifier —
AEROVOX WIRELESS CORPORATION.
121. FILTER CONDENSERS— Some practical points on the
manufacture and use of filter condensers. The difference be-
tween inductive and non-inductive condensers. Polyment
Mfg. Corp.
122. RADIO TUBES— Specifications and operating charac-
teristics of vacuum tubes. Twenty-four pages. E. T. CUN-
NINGHAM, INC.
123. B SUPPLY DEVICES— Circuit diagrams, characteris-
tics, and list of parts for nationally known power supply
units. ELECTRAD. INC.
124. POWER AMPLIFIER AND B SUPPLY — A booklet giving
several circuit arrangements and constructional information
and a combined B supply and push-pull audio amplifier, the
latter using 2 10 type tubes. THORDARSON ELECTRIC MFG. Co.
125. A. C. TUBE OPERATION — A small but complete
booklet describing a method of filament supply for a.c. tubes.
THORDARSON ELECTRIC MFG. Co.
126. MicRpMETRic RESISTANCE— How to use resistances
for: Sensitivity control; oscillation control; volume control;
regeneration control; tone control; detector plate voltage
control; resistance and impedance coupling: loud speaker
control, etc. AMERICAN MECHANICAL LABORATORIES.
Samson "Pam" Amplifier
Type PAM 16 is
for all ordinary
types of loud
speakers,
Type PAM 17 is
for and supplies
field current to
dynamic type
speakers.
Type PAM 16 or 17,
List Price $125.00 for 1 10 Volt, 50-60 Cycle A. C.
A
COMPACT, self-contained, rugged, all electric, two stage audio amplifier
for radio console or table. Designed to meet Underwriters' and A. 1. E. E.
standards. Compensation is made for line voltage variation. Approximate
undistorted power output 7 watts.
Due to the high standard of parts used in its manufacture, the question bf
service ends with its installation. Immediate deliveries can be made by your
jobber or dealer, or direct from us.
With the use of superlatives in radio advertising all too prevalent the best
guarantee of excellence in performance is the fact that Samson products have
been standard in the quality field since 1882.
\amson
General Offices: Canton, Mass. Factories, Canton and Watertown, Mass.
Manufacturer* since 1882
Complete stocks for the latest kits are always
sive Radio house and the largest distributors for
following kits and hundreds of other circuits are
instant shipment.
Silver-Marshall Shielded Grid Six
Silver-Marshall Screen Grid Laboratory Super
Silver-Marshall Hi-Volt
Silver-Marshall Unipacs and Pushpull Amplifiers
Rernler Infradyne
Remler Best Screen Grid Super
World's Record Super
Karas A-C Equamatic
New Bremer-Tully Power Six
711 WEST LAKE STREET,
QUICK SERVICE— PROMPT SHIPMENT
You can rely upon us to fill your orders promptly.
We have the very latest parts and complete stocks
always on hand. You can tie up with us for any-
thing in radio that you may need at any time.
SEND FOR FREE CATALOG NOW
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money-saver. Just mail the coupon and a complete
copy will be sent you.
CHICAGO, ILLINOIS
ALL THE LATEST KITS and PARTS
Send for 1 928 WHOLESALE DEALERS' CATALOG
Greatest Discounts on All Standard Parts, Kits, Accessories and Equipment
Dealers, set builders, and agents, send for this catalog. You will
find complete parts and equipment for the latest circuits featured
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RADIO BROADCAST ADVERTISER
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RADIO THEORY AND OPERATING. By Mary
Texanna Loomis. Chapters, 44. Pages, 886.
Illustrations 632. Loomis Publishing Company,
Washington, D. C. Price, $3.50.
RADIO Theory and Operating" is one of
the most comprehensive volumes so far
published in its field, covering not only
radio theory and circuits but also the necessary
electrical engineering required in the operation
of radio telegraph and radio telephone trans-
mitters and receivers.
The book is obviously a product of most ex-
tensive and painstaking research and reading,
and familiarity with the work of the best au-
thorities on radio subjects. <It is now issued, re-
cently revised, in its third edition.
There are two possible treatments of compre-
hensive works on radio subjects. A book may be
designed to appeal to the radio enthusiast who
desires to understand thoroughly the theory and
operation of radio. It may also be planned for the
professional radio man who studies the subject
as a member of a class conducted by an expert
teacher. Miss Loomis's book is decidedly in the
latter classification. Her treatment of the subject
is in a matter of fact and unromantic style. This
is not written in the spirit of condemnation, but
merely to define the author's point of view.
The work is divided into four parts. The first,
of twenty-five chapters, discusses the principles
of transmitting. There are seventeen chapters
dealing with the principles of electricity and
magnetism, generators, condensers, transform-
ers, and the essential parts of the radio trans-
mitter before we come to Chapter XVI II,
dealing with oscillating currents. Thus the
groundwork is thoroughly laid before radio cir-
cuit principles are considered. The second part
deals with receiving circuits, in eleven chapters;
the third, devoted to vacuum tubes and con-
tinuous waves, comprises six chapters; the
fourth, entitled "The Practical Radio Operator,"
covers that subject with eight chapters.
To substantiate my point that the book is
based more on reading and research than upon
practical experience in the handling of radio
equipment (not that the author is without ex-
tensive practical experience), this last section
quotes liberally and thoroughly digests the Gov-
ernment regulations applying to radio, abbre-
viations used in practice, message forms, traffic
regulations, and the forms used in practical ship-
to-shore operating, all material obtainable by
research and consultation of authorities. On the
other hand, when the author deals with troubles
which may be encountered in the operation of
transmitters and receivers, that clearness and
completeness which otherwise characterizes the
book is somewhat lacking. For example, the
operation of crystal control in broadcasting sta-
tions is disposed of in the following paragraph:
"When crystal control is used, too high a volt-
age must not be placed on the crystal, as this
may break it. From 300 to 400 volts appears to
be the limit that the crystal can stand. Crystals
are a great help in keeping the oscillation fre-
quency constant and, by eliminating wastes due
to wild oscillations, the radiation is increased.
However, the crystals are not imperishable.
They need care and have to be replaced occa-
sionally."
The same characteristic of treatment may be
observed in the discussion of possible troubles
with receiving sets:
"If upon sitting down to listen, on what ap-
pears to be a correctly wired receiving set,
nothing is heard, aside from the possibility of
an error in the circuit, this may be caused by
something very simple. The trick is to find the
simple cause. Perhaps the most common cause
of this is a short-circuited fixed condenser, either
shunted across the telephone circuit or the first
amplifying transformer. This may be caused
by the use of a hot soldering iron as a con-
denser composed of copper or tin foil and waxed
paper, is not intended to withstand heat. Where
fixed condensers are soldered into a circuit,
this must be done very cautiously. Probably the
next most important cause for silence in a re-
ceiving set is a poor contact between the prongs
on the base of the tubes and the springs in the
socket. Springs should press tightly against the
prongs," etc., etc.,
Considering that the volume is entitled
"Radio Theory and Operating" and not merely
" Radio Theory," possibly a better balanced
book would have been produced by more com-
plete and systematic arrangement of possible
troubles encountered in the operation of trans-
mitting and receiving apparatus.
Another peculiarity of the book is the meticu-
lous care observed in giving credit to independent
inventors whose work antedated those generally
given credit for radio's important inventions.
Unquestionably this attitude arises out of the
fact that Miss Loomis's father is Dr. Mahlon
Loomis, who demonstrated radio transmission
and reception in 1872, in Virginia. His pioneer
work is not generally recognized. A patent was
issued him on July 30, 1872, and his demonstra-
tions, a matter of public record, establish his
priority over Marconi. But history invariably
credits the man who first puts over a new idea
or system commercially, whether he is the first
inventor or not.
Doctor Loomis bears the same position in
radio that Dr. Samuel Langley holds in aero-
nautics. The Wright brothers are credited with
the invention of the airplane because they were
the first to demonstrate it to the general public
so that, through their influence, it has won recog-
nition as a practical device. Glenn H. Curtis,
substituting a modern motor for the steam
engine originally installed as motive power in
1897, made Langley 's plane fly successfully.
But even this vindication of Langley has not
deprived the Wright brothers of their position
as the acknowledged inventors of the airplane.
Miss Loomis's book is to be recommended
particularly to commercial wireless telegraph
operators. The chapters dealing with the care
of storage batteries, the functioning and care of
motor generators and power equipment, and the
regulations applying to commercial practice
are thorough and complete. An extensive series
of questions at the back of the book are helpful
in preparing for Government examinations.
Standard ship and commercial installations are
quite thoroughly dealt with. The volume is well
indexed and well arranged.
— EDGAR H. FELIX.
Another Text for Operators
PRACTICAL RADIO TELEGRAPHY, by Arthur R.
Nilson and J. L. Hornung, McGraw-Hill Book
Co., Inc., 380 pages, $3.00.
TH E preface to this book states that it is writ-
ten for radio students preparing to become
radio operators. Its scope is therefore marine
radio telegraphy, and does not include broad-
casting. At first it may seem that enough books
have been written to aid aspiring young electri-
cians to survive the terrors of the government
license examination, but this book really does
the job extraordinarily well; better, I believe,
than any previous work on the subject. The art
has changed, and most of the earlier treatments
RADIO BROADCAST ADVERTISER
BOOK REVIEWS
(Continued from page 56)
Practical Radio Telegraphy — Nilson and Hornung
are out of date. This fact, as well as the long
experience of the authors in the training of radio
operators, justifies the appearance of the present
volume.
The treatment begins with the physical funda-
mentals of the art, the first seven chapters being
devoted to such topics as magnetism, motors
and armatures, and characteristics of alternat-
ing current circuits. The treatment is nowhere
skimpy; in the chapter on armatures, for ex-
ample, the elements of armature winding are
fully described. Wherever physical principles
are expressed the atomic theory is used. Occa-
sionally the phraseology is a little dubious, as
in the discussion of dielectric breakdown on
page 107, where the authors tell us that "a rup-
tured insulator might be defined as a material
in which the electrons have been extended be-
yond their limit, or, in other words, the elec-
trons have been strained beyond the elastic
limit of the atomic structure. ..." A strained
electron might tax the conceptual powers of
greater intellects than those of average young
men studying to become brass pounders on the
high seas. But the explanations are in the main
clear and scientific; the one which has been
quoted is not a fair example.
Photographs and practical illustrations of ap-
paratus have been secured from manufacturers
and communication companies. Spark, vacuum
tube, and arc transmitters for marine use, com-
mercial receivers, and the radio compass, .are
thoroughly described. Questions at the end of
each chapter may be used by the student to test
his knowledge. Most of the chapters are written
to the length of a normal assignment in a radio
school. The printing is first-rate, with the ex-
ception of a comical error in the running head
of Chapter XXI. The book includes an index.
It is written for readers who lack preparation
in elementary electricity, mathematics, and
chemistry, gives them what they need of such
prerequisites, carries them through the tech-
nique of radio marine telegraphy, and fills the
need for a reference book for finished operators.
— CARL DKI-HI-K.
In sending the coupon below, make sure that your
name and address are included and are plainly
written.
USE THIS BOOKLET COUPON
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City. N. Y.
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This coupon must accompany every request. RB 5-28
THREE TIMES!
Type 587-A Power Speaker Filter
Phis instrument thoroughly insulates the speaker
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as any
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For the set owner who demands the best from his receiver, this instrument will provide
the maximum flexibility in home testing. Besides its adaptability for making B-eliminator
voltage adjustments, the Pattern No. 116 may be used for general test purposes as well.
The movement of Pattern No. 116 is a sensitive, D'Arsonval moving coil type, having
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pointer is provided with a zero adjuster.
Ask your dealer about it or write us for descriptive circular No. 1 103.
Jewell Electrical Instrument Company
1650 Walnut Street, Chicago
"28 Years Making Good Instruments"
58
RADIO BROADCAST ADVERTISER
Is Your Set
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AMERjRAN
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WESTERN RADIO MFG. CO.
134 W. Lake St. Dept 45, Chicago
DIRECT SELLING BY RADIO
Is It a Menace to the Retail Business Structure?
By Francis St. Austell
President, Iowa Radio Listeners' League
LIT in Iowa, the haunt of direct selling
by radio, all arguments for and against
"Direct Advertising" and "Indirect
Advertising" have been abandoned in favor of a
heated controversy on the subject of direct selling
by radio. Advertising, direct and indirect, has
in the case of some radio stations, given place to
urgent, persistent, forceful and vociferous clam-
oring for orders for all kinds of commodities.
The three terms, indirect advertising, direct
advertising and direct selling have been defined
as follows: Indirect advertising is the type of
publicity sent out by a great number of stations
including those on the networks. It consists of
the name of the advertiser who sponsors the en-
tertainment, with a mention of products in a
manner calculated to create good will and also
help all who are concerned in the merchandising
of those products. Direct advertising consists of
the broadcasting of requests for orders, with or
without price quotations sent out by a station
which has sold time to an advertiser for the
purpose of selling goods by radio. Direct selling
consists of the solicitation of orders by a station
which sells goods direct to the consumer for its
own account and for its own profit.
The center of the controversy is quite naturally
Iowa, because the principal direct selling stations
are located in that state. The writer is not famil-
iar with the situation in other states, but is
certainly very familiar with the Iowa station
which is probably unique or ought to be.
A half-hour period usually called the "Letter
Basket" has just been brought to a close by the
owner and operator of KFNF Shenandoah. This
station was the first to adopt the plan of selling
directly to consumers and is still the chief expo-
nent of the art. During the period referred to, the
public was begged to send orders for tires, dishes,
peaches.'coffee, Chinese baskets, pencils, fountain
pens (guaranteed for life) suits, overcoats, paint,
canned corn and nursery stock, not forgetting
prunes. Before the advent of radio, the owner and
operator of KFNF was in the seed and nursery
business. The other lines have apparently been
added since the issue of a license to broadcast.
KFNF, Shenandoah, is now self-announced as
the "merchandise center of the middle west"-
"the pioneer trading station" and somewhat
vaguely as "the world's largest." In a few short
years a business primarily devoted to seeds and
nursery stock, with an annual turnover of prob-
ably about three hundred or four hundred thou-
sand dollars, has grown with the aid of radio
into a business with a volume of more than
three million dollars.
The entertainment furnished by KFNF is not
of a high class nature. It is what is called common
music for common people or simply old-fashioned
music for plain folk. While the response from
the public to the efforts at entertainment is
meager, the response to the talks broadcast from
that station is enormous. These talks are really
clever and deal with agriculture, horticulture,
household hints and many other subjects.
KFNF has a following which numbers many hun-
dreds of thousands and every one of them will
fight if his favorite station is criticized. There
is probably no station in the country that has
such a loyal following and some extra bitter
opponents of direct selling say that no other
station wants such a following. The opponents
of direct selling are divided into two classes. One
class wants direct selling stations to be put off
the air entirely. The other would be content if
direct selling were abolished and would demand
nothing more.
Henry Field of KFNF, just plain "Henry" to
his friends, has a magnetic personality which
reaches out and grips his audience. His descrip-
tion of a cup of his famous coffee is tantalizing
and his vivid picturization of a cooked slice of
his wonderful ham just makes one's mouth water.
His coats are the best ever heard of, his overalls
are works of art, his tires make motoring a joy
forever, his canned peaches bring to our table
the sunshine of California. It is a bad day when
his sales talks do not bring a few thousands of
dollars to the merchandise center.
THE FINE ART OF RADIO SELLING
HENRY FIELD has developed salesmanship
by radio into a very fine art — so fine an art
in fact that many claim that if his example were
followed by others fortunate enough to own a
radio station, the whole retail business structure
of the country might be endangered. The selling
of merchandise by radio is so profitable that it is
surprising to find so few radio stations engaged in
the pastime.
Those who oppose direct selling as unfair
competition ask: " If one broadcaster is allowed
to use the greater part of his time on the air for
the purpose of soliciting orders, why should not
every broadcaster do it? Why should not every
man be given the right to erect and operate a
radio station, provided he expresses the willing-
ness or desire to sell prunes, peaches, tires, over-
alls and other commodities?"
At present, the local dealer who has no broad-
casting station is in an unfortunate position. He
is open to attack, direct, indirect, by accusation
and by innuendo. Not having a radio station from
which to shout, he is naturally at a loss for a
reply. He gets sore and thinks of all kinds of
smart "come backs," but he has to remain silent.
It is not unusual to hear over the air remarks
to the effect that "your local merchant would
charge you at least twelve dollars — but by buy-
ing from this station, you get it for seven dollars."
The purchaser by radio also has the extra and
exquisite pleasure of hearing his name "read
out." The price comparison, according to reports
from dealers, is not always fair or absolutely
correct, but who can contradict it?
KFNF sometimes issues statements to the effect
that the station does not undersell competitors
and claims "quality" as the keynote of its busi-
ness policy. At another time, the station claims
to have forced down prices on many commodities
and to have saved the farmer vast sums of money.
Whether or not they save money or get better
quality the loyal followers of Henry send their
cash to his station and demand that he be allowed
to do as he likes with his radio station.
It has been stated that the direct selling sta-
tions of Iowa can produce five hundred thousand
signatures to support their claims to popularity.
This is no doubt a very low estimate. But it may
be asked whether the popularity of a station is
sufficient excuse for what many regard as the
evils of direct selling. On this subject a correspon-
dent remarks " popularity has nothing to do with
RADIO BROADCAST ADVERTISER
59
THE OFFICIAL
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THE world-wide fame of Brown-
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BROWNING
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BAKELITE— HARD RUBBER
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DIRECT RADIO SELLING
by Francis St. Austell
(continued from page 58)
it. Saloons were popular once, but where are
they now?" Correspondence comes from all over
the country, from Rhode Island to California,
from Maine to New Mexico, and it is a very note-
worthy fact that most letters from opponents of
the principles of direct selling are on excellent
paper and represent a highly educated class,
while those from supporters of the direct seller are
for the most part, extremely hard to read, are
not noted for cleanliness and usually avoid refer-
ence to the real subject of debate. The popularity
of KFNF is based on its talks, its gospel hymns,
religious services and its old-fashioned music.
The opponents of direct selling do not necessarily
criticize these features, but the loyal followers of
KFNF see in an attack on direct selBng.-a camou-
flaged attack on the gospel. They want Henry
or "Henery" and resent any suggestion of criti-
cism, even of the station presided over by their
idol. The owner and operator of KFNF recently
broadcast a statement to the effect that those
who did not like his station were writing to the
Federal Radio Commission, telling that body
all about it. He also commented on the fact that
these people were sending typewritten letters.
The young lady who sorts my mail was discov-
ered once making two piles of letters before open-
ing them. One was a clean, neat pile, the other
was quite different. When asked the reason for
such a procedure, she remarked "The clean ones
object to direct selling, the dirty letters support
it." Quite simple, but also very significant. Of
course their are some very clean and well written
letters favoring direct selling but these are con-
spicuous in comparison.
WHERE DIRECT SELblNG IS POPULAR
AT A convention in Des Moines, held last
year, a speaker attacked the principles of
direct selling, without mentioning any stations
by name. Mr. Field of KFNF requested that bar-
riers be let down and that the matter be dis-
cussed openly, as he said he was quite aware the
remarks referred to him. The way followers of
Shenandoah rallied to his support was an eye
opener to many. Women, who would ordinarily
dread the ordeal of a public appearance, spoke
fearlessly and eloquently, facing with real de-
termination a crowded convention hall. Farmers
and their wives told of what Henry had done for
them, and they left not the slightest doubt as to
the popularity of Henry Field among his im-
mediate followers. To his opponents, he repre-
sents probably the most unpopular station in the
world. Popularity is not the right word. This
man, Henry Field, arouses a feeling among his
followers that is akin to worship. He is becoming
a cult. The reasonable opponents of direct selling
do not hesitate to give him credit for all the good
things he has done. They fight with him on the
points only of direct selling and the methods em-
ployed in merchandising.
All the foregoing remarks can be applied to
other stations, of course, as far as merchandising
is concerned; but the magnetic personality of
Henry Field makes him stand alone, a national
figure, a creation of radio, a leader of hundreds
of thousands, almost a prophet, a Moses of the
common people.
It would seem that the direct selling stations
sometimes act as agents for manufacturers and
merchants, while certain commodities are bought
outright and sold by the station which is in real-
ity a mail order house, with a catalog and also
the additional advantage of having a radio
station from which to broadcast bargains. All
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wave rectifier is absolutely dry. No water . . . no acid . . .
no alkali ... no tubea ... no electrolytic action. Nothing:
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Assemble In Half an Hour
Everything- supplied, even to the screws, wire, drilled
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operated from the same switch.
Big Prollts for Set Builders
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builders of America, for a limited time only, a money-
savin ir plan which is nniqne in thf annals of radio. Send
the coupon today, before it is too late.
KNAPP ELECTRIC CORPORATION
Port Chester,, N. Y.
Mil. ItAVlD W. KNAPP, Pres., Knapp Electric Corporation
333 Fox Island Hoad,
Port Chester, K. Y,
Send me complete information rejrardtncr the Knapp "A"
Power Kit and your special discount to set Builders.
Name
Address
60
RADIO BROADCAST ADVERTISER
NEUTRODYNE
1. Single Unit AC Jewelbox, $05. Genuine neutrodyne
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Crosley radios are adaptable to any type of console installa-
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THE CROSLEY RADIO CORPORATION
Powel Croeley, Jr., Pres. Cincinnati, Ohio
Licenned only for Rnriio Amateur, Experimental and Broadcast
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RADIO
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DIRECT RADIO SELLING
by Francis St. Austell
(continued from page 5p)
goods are sold with a money back guarantee.
Even the hams can be cooked, partly consumed
and the remainder sent back if not satisfactory.
As an indication of the volume of business done
figures recently broadcast from one of the so-
called "farm stations" are given here. They in-
dicate sales since February, 1927.
55 carloads of tires — 400,000 pounds of coffee
— 100,000 overalls and jackets, 30,000 work and
dress shirts, 70,000 dress patterns of j-J- yards
each — 10,000 ready made dresses — 24 carloads
of prunes — 60,000 pairs of silk stockings — 50,000
radio tubes — 3000 suits and overcoats since
October 1927; that represents only a part of the
business of one radio station. To the writer, the
figures do not appear in any way exaggerated.
Retail merchants are becoming alarmed, fol-
lowers of the farm stations are elated. The so-
called farm stations claim the support of farmers
as a class. One farmer writes and states plainly
that it is a damned lie to say that all farmers are
in favor of direct selling. Another is equally posi-
tive that farmers are all for it.
That broadcasters themselves are not entirely
united on the subject of direct selling is indicated
by the following quotation from a letter ad-
dressed to the writer by the secretary of the
Berry Seed Company, which owns and operates
station KSO, Clarinda, Iowa, This station was en-
gaged in the direct radio sale of seeds and
kindred lines. The letter says, in part:
"The question of direct selling or the
quotation of prices over the radio is one that
is receiving much discussion not only in Iowa
but in many other sections of the United
States. . . .We cannot help but come to
the conclusion, after considering the matter
from all angles, that it does give such firms
an undue advantage over competitors who
have no radio station or access to one over
which their prices may be quoted. This
might readily be termed an unfair advantage
and perhaps for that reason alone should be
eliminated. . . . To return to our former
statement, we would welcome an order to
desist from quoting prices. We welcome a
mutual agreement that would eliminate it,
and if neither of these occur, we shall perhaps
cease anyhow."
An ardent supporter of direct selling principles
was asked by the writer if he could produce one
logical argument in favor of it, merely said: "The
broadcaster was lucky and he found a gold mine
in a radio station. There is no law against using
a gold mine."
There is no law to prevent a man from being
lucky enough to find and use a gold mine, but
unfortunately, there is a law which prevents a
lot of people from founding a broadcasting sta-
tion. One station of the direct selling kind, accord-
ing to its own report, annually sends out cata-
logues to the number of a million and a half.
The follow-up to these catalogues consists of
direct selling talks by radio. Catalogues from
other firms must be followed up by mail. It looks
a bit one-sided, doesn't it?
The Radio Commission announces that it has
not been given the power to dictate to a broad-
caster whether or not he should sell and puts the
matter up to the public.
Let the public decide — as quickly as possible.
IAET
NEW
Adapter Harness
Makes possible the usins of now
A. C. tubes in present set with-
out any structural alteration.
Chanpe ean be made in ten min-
utes. Eliminates "A" batteries.
Use your present "B" and "C"
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1RTHUR H. LTNCH. Inc.. 1775 Bco.wdw.r, N r. C.
How Does Your Receiver
Work?
What Antenna is Best?
How Radio Tubes Func'
tion?
These questions and many others
are answered in Walter Van B.
Roberts' book, "How Radio Re-
ceivers Work."
Today — send one dollar, for your
copy, to the Radio Broadcast Book-
let Dept., Garden City, N. Y.
1928 Edition, com-
plete, up-to-date.
Full information
on A. C. and Screen
Grid Tubes. Over
90O pages, 1025 illiu-
trationi. For Service
and Repair Men,
Dealer*, Salesmen,
Experimenter* and
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or by mail, $6.00.
FREDERICK J.DRAKE fc-CO.
Michigan Ave. Chii
RADIO BROADCAST ADVERTISER
61
5 -Prong S-M
Plug -In Coils
Economy — Efficiency
For the popular "tube base" short wave receiver Silver-Marshall will have
ready on June 1st, new types of moulded Bakelite coil forms and wound coils
designed to fit any standard 5-prong tube socket, such as S-M 512. These forms
have ample winding space for all short wave or broadcast band coils, and a
tickler slot at the base. Their small size particularly adapts them to short wave
sets to provide the smooth regeneration necessary to telephone or rebroadcast
reception and their cost Is as low as their efficiency and flexibility is high.
Type 130 blank forms can be had with smooth winding space I'/i" In diameter
and 1^" long, with tirkler slot and pins at .50 each, or wtth threaded winding space (98 threads) If preferred. A variety
of typel wound for different purposes can be had at $1.25 each list. Type 512 socket which fits these coils is priced at 75c
Why pay $8 00 to *!'' 01) for a set of short wave colls when four 130 forms and a 512 socket costing $2.75 altogether
plus less than a pound of' wire and an hour's fun will give you as pretty a little set of coils, tuning from 17 to over 200
meters, as you'd evec want to see.
The Famous S-M 240 Audio Transformer
WTO I1J*1M afOi leaui-i in INI- .iuun> utivt u* imv unvii „ ,v»_i — •-•• —r- - - — ~
quality in any set you buy or build. Price, 240 audio, 3:1 ratio, $b.OO; 241 output,
ABC and B Power Units to Fit in Your Set Cabinet
ready to assemble $92.75.
SILVER-MARSHALL, Inc.
SILVER-MARSHALL. Inc., 838 West Jackson Blvd., Chicago, III
I enclose :0c for which please send me full Information on the S-M
audio transformers, power supply units, unlpacs, and the h-M receivers.
..I enclose 25c for instructions for building the S-M unlpacs.
.... enclose 25c for Instructions and blueprints (or building the Shielded
....I enclose 2 5c for instructions and blueprints for building the S-M
wave tuners.
The new S-M "670" Reservoir Power Units are but 13" long.
3%" wide and « V4 " high over the 280 rectifier tube they use. Both
are housed in attractive brown crystaline steel cases, and have the
features that made the older 652 and 656 Reservoir B's the most
popular kits of their type. The Clough selective flitter and a new volt-
age divider system provide unusually <iuielness and freedom from motor-
boating on any set of one to ten tubes. 670B supplies filed voltages of
"""A 90 135 and 180 to 200 volts, with a variable tap giving from 22 V4
to 90 volts. 6 70 ABC supplies the same B power and A and C power to any
AC tub! Sl'i ' 5 volts' 2 25 and 5-° volts A for up to seven tu
iMOMHrr C bias for the tubes used obtained by suitable resistors In the set
K70B is priced at $35.50 wired, ready to use, or $33.00 in kit form, with
cabinet ready to assemble. 670ABC is priced at $38.50 wired, or $3a.OO
for the complete kit with all instructions.
New Unipacs for 250 Tubes
Two Unipacs taking full advantage of the new 250 type tube are ready, one
a single stage Unlit socket power amplifier and B supply, and the necnd a
wo stage amplifier for radio or phonograph. Each uses one UX-250 amplifier
tube to furnish 4«T)0 milliwatts of undistorted power output, which means just
about the sweetest fullest tone you've ever heard — just a shade belter than
838 West Jackson Blvd., Chicago, Illinois
R.uno BHOADCAST. June.
Published monthly. Vol. XIII. No. 2. Published at Garden City. N. Y. Subscription price $-1.00 a year. Kntered at the post office at
Garden City. N". Y.. as second class mail matter. Doubleday, Doran & Company. Inc.. Carden City. N. Y.
RADIO BROADCAST
JUNE, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XIII. No. 2
Cover Design - - From a Design by Harvey Hopkins Dunn
Frontispiece In the Grand Canyon of the Colorado
How Chain Broadcasting Is Accomplished - - - - C. E. Dean
The March of Radio - An Editorial Interpretation
Broadcasting Needs Capable Leadership
Mergers in the Radio Industry
More High Power Broadcasting
British Skeptical of Baird Television Accorri'
plishments
Present Distribution of Broadcast Stations
Here and There
Automatic Tuning for the Radio Receiver -
The Newest Power Tube
Book Reviews
Leroy S. Hubbell
Howard E. Rhodes
Carl Dreher
Lefax Radio Handbook
Radio Engineering Principles, Lauer and Brown
A Popular Guide to Radio, Dashiell
The "Cornet" Multiwave Receiver - - - - W. H. Wenstrom
From Milliammeter to Multi'Meter - - - - - G. F.
"Strays" from the Laboratory
Output Transformer Characteristics
High Powered Press Releases
A.C. Troubles
May Standard Frequency Signals
Short-Wave Notes
Recent Interesting Contemporary Articles
Another Useful Publication
Radio School Scholarships
New Apparatus - - Useful Information on J\[ew Products
A Screen-Grid Booster for Any Receiver - Glenn H. Browning
Our Readers Suggest
An Emergency Detector B Supply
Emergency and Experimental Connections
Volume Control for Resistance-Coupled Am-
plifiers
Some Baffle-Board Experiments
Antenna Tuning Device
A Spark Plug Lightning Arrester
"Radio Broadcast's" Service Data Sheets on Manufactured
Receivers '*''*'
No. i. The Amrad A.C. 7 No. i. The Pfansteihl A.C. 54 and 50.
Building and Operating the A. C. "R. B. Lab" Receiver
Hugh S. Knowles
Using the Screen-Grid Tube in Popular Circuits Laboratory Staff
A Good Crystal Receiver for the Beginner - - Keith Henney
A Three-Tube A.C. Operated Roberts Receiver Elmer G. Hery
As the Broadcaster Sees It Carl Dreher
The Simplest Receiver
Design and Operation of Broadcasting Stations:
ao. Field Strength Measurements
The Listeners' Point of Vieu>
The Month's New Phonograph Records - - *
"Radio Broadcast's" Directory of Vacuum Tubes
Manufacturers' Booklets
"Radio Broadcast's" Laboratory Information Sheets
No. 193. Motorboating
No. 194. Push-pull Amplifiers
No. 195. A Resistitnce'Coupled Amplifier
with Screen-Grid Tubes
No. 196. Circuit of a Resistance-Coupled
Screen-Grid Amplifier
The Haven of a Sea'Going Audion
No. 197. Amplification Constant
No. 198. The Screen-Grid Tube as an R.F.
Amplifier
No. 199. Current
No. 200. Resistors
64
65
68
72
74
76 /
77
80
83
85
87
89
93
96
97
99
1 02
How Can Good Radio Programs Be Created? - John Wallace 104
106
107
108
no
Raymond Travers 116
I AMONG OTHER THINGS.
IT HAS not been possible to reply with a personal letter to
each of our readers who filled out and returned the readers'
questionnaire recently sent many of those who are regular sub-
scribers. The desires and opinions of readers expressed have
been very helpful. Many interesting conclusions are at once
apparent. Our policy of giving complete information about the
manufactured parts described in constructional articles is over-
whelmingly approved. The type and form of the articles dealing
with the construction of apparatus — such articles as those in
this issue for example — are welcomed. The many special features
and articles which distinguish RADIO BROADCAST from its con-
temporaries are especially praised.
SOME readers who have read elaborate statements of policy
appearing in some of our contemporaries have asked us, in
effect, if we were going to announce a changed policy, too. All
we have to say about the editorial policy of RADIO BROADCAST
has been said in this column in the May issue. This magazine is
edited for the reader and what he finds in RADIO BROADCAST is
information — lots of it, as interestingly, as completely, as accu-
rately presented as we know how. This magazine will neither be
full of inconsequential and slightly sensational articles about the
marvelous potentialities of radio nor will it overflow with con-
structional articles on every possible subject having the appar-
ent purpose of merely using the products of a selected group of
radio manufacturers. Our policy of making each article complete
in itself and not "continued on page 06" is still in force. The
special sections which have so wide a following: the Laboratory
Data Sheets, the March of Radio, Strays from the Laboratory,
Our Readers' Suggest . . . , As the Broadcaster Sees It, the Serv-
ice Department, are to be continued. With this issue, we intro-
duce a new regular feature: "RADIO BROADCAST'S Service Data
Sheets on Manufactured Receivers" which present all essential
data on various makes of sets now in use. Several other impor-
tant new features are in the course of preparation.
EDGAR H. FELIX, contributing editor, attended the pub-
lic hearings before the Radio Commission April zj and
14. He appeared as an expert witness and presented the sugges-
tions for the solution of the broadcasting problem which have
attracted such wide attention in our editorial section. The
March of Radio. Incidentally, we are told that Mr. Felix's May
article "Will New Transmitting Methods Be the Remedy''" is
accepted in Washington as the most clear and fair presentation
of the difficulties and possibilities for solution of the present
broadcast situation.
OUR July issue promises many interesting features. There is
an excellent non-radiating short-wave receiver using a
screen-grid tube, a searching analysis of the almost overwhelm-
ing obstacles to practical television, the description of a fine B
supply and power amplifier using the 250 type tube, a practical
set tester, and many other articles, selected because of their
unusual interest.
— WILLIS KINGSLEY WING.
The contents of this magazine is indexed in The Readers' Guide
to Periodical Literature, which is on file at all public libraries.
OOUBLEDAT, DORA^ & ^OMPA^T, D^C., Garden Qity,
MAGAZINES
COUNTRY LIKE
WORLD'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
SHORT STORIES
EDUCATIONAL REVIEW
LE PETIT JOURNAL
F.L Eco
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WEST
THE AMERICAN SKETCH
ROOK SHOPS (Books of all Publishers)
LORD & TAYLOR; JAMES McCREERY & COMPANY
PENNSYLVANIA TERMINAL AND 166 WEST 32ND ST.
NEW YORK: 848 MADISON AVE. AND 51 EAST 44TH STREET
420 AND 526 AND 819 LEXINGTON AVENUE
GRAND CENTRAL TERMINAL AND 38 WALL STREET
CHICAGO; 75 EAST ADAMS STREET
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OFFICES
GARDEN CITY, N. Y.
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LONDON: WM. HEINEMANN, LTD.
TORONTO: OXFORD UNIVERSITY PRESS
OFFICERS
F. N. DOUBLEDAY, Chairman oj the Board
NELSON DOUBLEDAY, President
GEORGE H. DORAN, V ice-President
S. A. EVERITT, y ice-President
RUSSELL DOUBLEDAY, Secretary
JOHN J. HESSIAN, Treasurer
LILLIAN A. COMSTOCK, Assft Secretary
L. J. McNAUGHTON, Asrft Treasurer
Copyright, 1928, in the United States, Newfoundland, Great Britain, Canada, and other countries by Doubleday, Doran fi* Company, Inc. All rights reserved.
TERMS: $4.00 a year; single copie* 35 cents.
62
RADIO BROADCAST ADVERTISER
Protect yourA-C tubes
from high line voltages
'with
t
Ward Leonard Vitrohm
Resistors and Rheostats
Radio receivers, made for complete operation from the
power lines, are designed, usually, to operate at a fixed
line voltage. Where the line voltage exceeds the arbi-
trary value assumed by the set manufacturer, damage to
the tubes may result unless means are used to reduce
the line voltage to the value at which the set is designed
to operate.
Two methods are used, ordinarily, to correct for exces-
sive line voltages; a resistor or rheostat placed in series
with the input to the power unit of the receiver. The
resistance value and current carrying capacity of these
units is determined by the receiver primary current and
the maximum potential drop required.
Vitrohm Resistors, fitted with Edison medium screw
bases, are the most convenient units to use where fixed
resistance is desired. These resistors screw into a series
tap which is in turn plugged into the convenience outlet
or socket. They are priced at $2.00 each and are avail-
able in the resistances listed below:
Catalog
Number
Resistance
In Ohms
Catalog
Number
Resistance
In Ohms
507-96
2.5
507-97
15
507-39
3.5
507-98
22
507-41
5
507-99
31
507-43
7
507-100
45
507-44
10
507-101
62
507-45
12.5
Vitrohm 4-inch, 11 step, Rheostats are used where
adjustment of voltage is desirable or necessary. Mount-
ing may be either front or back of panel. The price is
$5.50 each.
Catalog
Number
Maximum Resistance
In Ohms
507-83
507-59
507-63
12.5
20
50
Your dealer stocks Vitrohm Resistors and Rheostats, or can
get them (or you. Circular 512 describes methods of line
voltage control and shows complete diagrams of circuit con-
nections. It will be sent to you promptly upon request
without charge.
WARD LEONARD ELECTRIC CO.
MOUNT VERNON, N.Y.
RESISTOR SPECIALISTS FOR MORE THAN THIRTY-SIX YEARS
/n //*e Grand Canyon of the Colorado
A PORTABLE radio receiver in use in the
Grand Canyon in 1923. A special receiver was
built for the expedition by the Bureau of Standards
which was carried on a geological survey of the
Canyon under the auspices of the United States
Geological Survey. This illustration is from a photo-
graph by Lewis R. Freeman, of the Explorers' Club,
New York, who was a member of the expedition.
Mr. Freeman explains that at the time the expedi-
tion was undertaken, there was some doubt as to
whether radio reception would be possible in the
Canyon. It was conclusively demonstrated that
excellent reception was possible. The receiver per-
formed as well at depths of 500 feet as at 5000, Mr.
Freeman says. The antenna in the illustration also,
it seems, served the party as a clothesline.
64
CHAIN broadcasting is known to
radio listeners as a means whereby
a radio program may be transmitted
by several or even dozens of radio stations.
Regular networks furnish entertainment
every day, and on important occasions
great extensions are made so that prac-
tically the entire United States is covered.
The estimated audiences at such times
include one fourth to one third of the
entire population of the country. More
people have thus listened to the voice of
one person than ever before in history.
The apparatus and methods whereby
such important and remarkable results are
accomplished are, therefore, interesting
subjects to the radio fan. His knowledge of
vacuum tubes, audio-frequency amplifiers,
and electrical principles will enable him
to appreciate various interesting points in
the equipment and operation of the wire
lines used in chain broadcasting.
In addition to the long lines connecting to
radio stations in distant cities, there are
many shorter lines transmitting programs,
such as from studios centrally located in
large cities to the powerful radio broad-
casting apparatus out beyond the suburbs.
Similar circuits are used to broadcast
sporting events, banquets, and other occur-
rences outside the studio, thus greatly ex-
tending the range of program features.
It is one of the duties of telephone en-
gineers and operating men to plan and
supervise both the short and long lines
which carry radio programs. These con-
nections differ in various respects from
regular local and long distance telephone
lines, and have, therefore, been given a
special name, "program circuits." One
difference is that ordinary telephone circuits
transmit the voice- in both directions (on long
circuits" two-way "amplifiers are therefore neces-
sary), but in program circuits it is necessary to
transmit only in one direction, that is, from the
pick-up microphone to the one or more radio
transmitting stations. "One-way" repeaters are
therefore sufficient. In the drawing on page 66
arrows indicate the diiection of transmission
along each program circuit which was used on
January 4th, 1928, the date of the first Dodge
Brothers program. The regular route of the voice
of \\ ill Rogers, acting as master of ceremonies at
Los Angeles, may be followed by way of San
Francisco and Denver to Chicago and the East.
\lso an additional circuit for use in case of emer-
gency is seen passing through southern New
Mexico, Dallas, and St. Louis to Chicago.
MEETING THE TRANSMISSION REQUIREMENTS
ANOTHER important difference between
** ordinary telephone circuits and program
circuits is in the width of the frequency band
transmitted. In a telephone conversation, clear,
intelligible speech is desired, and it has been
found that this can be obtained if frequencies
from about 300 cycles per second to about 2000
cycles per second are transmitted, although
modern telephone circuits are engineered to carry
a somewhat wider frequency range. However,
with program circuits, not only satisfactory in-
telligibility is desired, but also a very high degree
of naturalness and faithfulness in the transmis-
sion of music and speech when reproduced
through loud speakers. To meet these require-
ments, a much wider band of frequencies is neces-
sary. In the present art it is generally considered
desirable to transmit a range of frequencies from
about 100 cycles per second to about 5000 cycles
per second, and to do this with approximately
uniform efficiency. In this way the low, medium
How Chain Broadcasting Is Accomplished
By C. E. Dean
American Telephone and Telegraph Company
THE CHAIN BROADCASTING CONTROL ROOM IN CHICAGO
Similar control rooms are located in Boston, Cincinnati, Detroit, St. Louis, Atlanta, San Francisco, and New
York, each in charge of a "transmission supervisor." Repeaters, oscillators, equalizers, transmission measur-
ing devices, and other apparatus necessary in the exacting work of transmitting the programs are shown in
the illustration. Cone loud speakers are mounted in the protecting frames at the left. During operation, one
cone is connected to the Red network, another to the Blue, a third to the Purple; the fourth is a spare.
and high pitch ranges of music and other program
material are transmitted with a considerable
degree of faithfulness.
In addition to the wider frequency-range
requirements, program circuits are called upon
to transmit greater volume variations than ordi-
nary telephone circuits. For example, the music
of a symphony orchestra will vary from a very
loud intensity, when many instruments are
sounding, to a very faint intensity at other times.
What Radio Owes to Chain
Broadcasting
THE Washington air, in and near the
halls of Congress, has been full of
pointed and often unpleasant comments
about chain broadcasting during the recent
weeks when the last radio bill was under
consideration. Aside from the political
aspects which so fascinate our legislators, it
can be said without fear or favor that chain
broadcasting is responsible almost entirely
for the growth of high-grade programs in
this country. Chain broadcasting has par-
tially solved the old question: "Who is to
pay for broadcasting?" As the use of the
wire network, linking stations, has in-
creased, so has the radio audience, and
with it the time, money, and effort ex-
pended on programs. This article explains
some of the technical aspects of the accomp-
lishment, much of which appears for the
first time.
— THE EDITOR.
At all times extraneous noise on the circuit must
be slight in comparison with the volume of the
music. The critical times are during the faint
portions of the program, and to transmit these
satisfactorily, a very quiet circuit is obviously
necessary.
The large variations in the volume of orches-
tral music (which are of the order of 50 TU, an
energy ratio of 100,000) are greater than radio
stations can transmit without overloading on
the loud signals and losing the faint portions in
local noise, static, etc., at the receiver. So at the
microphone amplifier one of the broadcast
station control operators manipulates the ampli-
fication control so as to reduce these variations,
cutting down somewhat the loud portions and
bringing up somewhat the faint portions, taking
care to preserve as nearly as possible the natural-
ness of the music. The program circuits, i. e., wire
lines are quiet enough to be able to more than
handle all the volume variation which the broad-
casting radio stations desire to transmit.
Besides the requirements just considered, the
program circuits must of course function har-
moniously with the other circuits of the telephone
plant, so that program transmission will not be
overheard on the ordinary circuits, nor vice
versa.
For short connections in cities and at other
places, circuits in cable are usually employed.
The attenuation, the loss, introduced by a
seven-mile length of iq-gauge cable pair (con-
sisting of No. 10 B & S copper wire), with no
loading coils or other apparatus connected,
increases considerably with increase of fre-
quency. One TU of loss means a reduction of
power to 795 per cent, of its original value, two
transmission units means a further reduction to
79$ per cent, of what is left, or to .795 x .705
.63 = 63 per cent, of the original amount.
66
RADIO BROADCAST
JUNE, 1928
Three TU is a power ratio of 50 per cent., four
is 40 per cent., and five TU 32 per cent. Twenty
TU is a power reduction to o.oi or I per cent,
of its original value, as shown by the bottom
line of the chart. (TU are also used to express the
amount of amplification, or "gain," of an am-
plifier, the ratio being the reciprocal of that for
loss. Thus, 20 TU gain is .ojr = 100 times, mean-
ing that the output power is 100 times as great
as the input power. For further information on
TU see Martin, Journal, A. I. E. E. June, 1924).
If the cable mentioned were used without
any correcting agency there would be a serious
reduction in the strength of the high-pitch com-
ponents which give music its charm and bril-
liancy. But frequency distortion, if not too great,
can be offset by introducing an opposite distor-
tion, a veritable case of two bad elements com-
bined to achieve the desired good result.
To correct the frequency characteristic of
short cable, special devices called "equalizers"
are used. These consist of inductance, capaci-
tance, and resistanre, three of the elements
forming a parallel resonant circuit, such as is
familiar to radio amateurs from its use as a
wave-trap. However, here the elements are so
chosen that the resonant frequency is far lower,
lying a little above the range of frequencies
which the circuit transmits. As in a wave-trap,
the impedance is high at the resonant frequency,
so that here the equalizer introduces little loss
since it is shunted across the line. But at lower
frequencies the impedance is much less, and by
proper adjustment of the two resistances and
the equalizer is made to have characteristics
just the opposite of those of the cable pair. The
resulting curve for the cable with the equalizer
is practically horizontal, which is the result de-
sired. The volume is then raised to a higher
level by a distortionless amplifier.
For the long connections between cities in
chain broadcasting, "open wire" circuits are
largely used, that is, circuits consisting of wire
on insulators supported by cross arms. Most of
this wire is hard-drawn copper (No. 6 B. & S.)
0.165 inches in diameter, the most rugged type
of open wire line used in the Bell System. The
energy loss along this type of line is much less
than along an equal length of the cable just
considered, but after the current has traveled
about two or three hundred miles it must be rein-
forced. For this purpose an audio-frequency am-
plifier, called a "repeater," is used.
An open wire circuit is similar to cable in that
the energy loss is greater at high frequencies,
but somewhat different methods are used to
make the open-wire frequency characteristic
horizontal. Repeaters which introduce greater
amplification for the high frequencies are used
in conjunction with equalizers. These equalizers
are different from the cable equalizer since the
conditions are not the same.
TELEGRAPH AND AMPLIFIER ARRANGEMENTS
PARALLELING every long program circuit
is a telegraph circuit over which reports and
instructions are transmitted. With keys and
sounders at every repeater station this provides
an auxiliary communication channel for the use
of those responsible for the program circuit.
Other telegraph circuits connect the radio sta-
tions on each chain with the key station for the
coordination of station announcements and other
program details.
One of the most interesting features of a pro-
gram network is the means employed to restrict
the effect of an accidental short-circuit of the
line at any point. Without the methods used,
such a short-circuit, besides preventing any
transmission beyond the particular point, would
greatly reduce the voltage for a considerable dis-
tance back along the line. Now an amplifier, be-
sides its primary purpose, has the important
property that a change in the condition of the
output circuit (such as a short), has practically
no effect on the input circuit. So, wherever a
program circuit forks, an amplifier is inserted
into each outgoing branch, with the result that
a short-circuit across one branch will not affect
the transmission along the other branch. This is
done regardless of whether or not amplification
is needed — the one-way feature of an amplifier
is taken advantage of in this way to increase the
reliability of the system. For this reason re-
peaters average about 125 miles spacing in the
East, when otherwise two or three hundred miles
would be sufficiently close, for there are numerous
forking points in this part of the country.
The drawing on page 67 illustrates, by a typi-
cal case, the manner in which the power decreases
along each section of a program circuit and is
built up to its original value at the repeater
points. For example, at the New York repeater
station the incoming power from the radio
studio is given a net amplification of 9 TU, and
then begins the trip to Troy, New York.
CHAIN BROADCASTING CIRCUITS OPERATING
ON EVENING OF JANUARY 4. 1928.
Otute used hx Dcdgf Brother Program
••""••- Cimjrts used only !w otfwt Program!
Tolal about 24.030 mite ol atari or 44000 mi!«
Conrwded radio station «ere wealed *i each city sho-n
Along the circuit the power decreases steadily
until at Troy it is only 3 TU above the origi-
nal input at New York. Here it is amplified
again, and continues on toward Syracuse
The maintenance of a horizontal frequency
characteristic, the importance of which has
already been stated, necessitates the introduc-
tion of losses at the repeater points which are
offset by amplification; for simplicity these are
not indicated, the net gain at each repeater
station being shown. The final output power
of the circuit at Chicago is seen to be four
times greater than the input power at New
York. The scale at the right gives for any
point the number of TU by which the power at
that point exceeds the input to the circuit at
New York. The left scale gives the correspond-
ing power ratio.
THE AMPLIFIERS OR "REPEATERS"
f^\f COURSE, the transmission of music and
^-' speech over program circuits is by alternat-
ing currents having frequencies the same as
those which are present acoustically in the sound
at the microphone. So the repeaters in the cir-
cuit are audio-frequency amplifiers. At the end
of each program circuit in chain broadcasting is
a radio transmitting station which sends the
program out on the ether at a radio frequency.
Special study has been devoted to the design of
telephone repeaters, and various types have been
developed. Those used in program circuits are
two-stage, transformer-coupled amplifiers using
130 volts plate supply. The first main element of
the repeater is an input transformer whose sec-
ondary is tapped to allow adjustment of the
amplification given by the repeater. The tapped
voltage from this transformer is applied to a
high-mu tube having an amplification factor of
about 30, and an output resistance of about 60,-
000 ohms. From this tube the energy goes
through an inter-stage transformer to the second
stage. Here there is a tube having an amplifica-
tion factor of about 6 and an output resistance
of about 6000 ohms, similar to the 2i6-A
or 1 12 type tubes which have been used in other
amplifiers. There is an output transformer for
delivering the amplified energy to the outgoing
program circuit. Provisions are made for close
adjustment of amplification and for adjustment
of the frequency characteristic. The amount of
amplification or "gain" in the repeater may bead-
justed to any value overa range of 37TU in steps
of as little as 0.3 TU so that very accurate setting
is possible. At 1000 cycles this adjustment varies
the gain from 5 TU to 42 TU, which is the same
as varying the power amplification from 3.2 to
1 5,800, or the voltage amplification from 1. 8 to 126.
TESTING AND OPERATION OF PROGRAM CIRCUITS
A FEW years ago the testing and operation of
•^ all the program circuits then in use was in
charge of one "transmission supervisor" located
in New York. Since then, the extent of program
circuits has grown by such bounds that it has be-
come necessary to have additional transmission
supervisors, and these are now located at Boston,
Cincinnati, Detroit, Chicago, St. Louis, Atlanta
and San Francisco. Each transmission supervisor
is responsible for the program circuits going out
from his control point. He, therefore, has charge
of hundreds of miles of circuits and a number of
repeater stations, through which the circuits pass.
At each of the repeater stations there are trained
men who are on duty during the hours that the
program circuits are being tested or used, and
these men make reports to the transmission sup-
ervisor, as directed, and adjust their apparatus
in accordance with his instructions.
It is very important to maintain the prograrr
circuits in the best of condition, for manv thou-
JUNE, 1928
HOW CHAIN BROADCASTING IS ACCOMPLISHED
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MAP SHOWING ROUTE OF CIRCUIT
WHAT HAPPENS TO ENERGY IN WIRE CIRCUITS
How the voice-frequency currents are attenuated as they travel over long
lengths of wire. Note the effect of amplification at the repeater points
sands of radio listeners are dependent upon them.
Each transmission supervisor, therefore, con-
ducts every morning a thorough test and ad-
justment of all the circuits under his charge.
Transmitting a tone of 1000 cycles over the
program circuits, he receives reports by tele-
graph and directs adjustments at the nearest
repeater station, then at the next repeater sta-
tion, etc., until, in this way, the entire group of
circuits under his charge is "lined up." Then a
low frequency, about 100 cycles per second, is
transmitted and any necessary auxiliary adjust-
ments are made to see that this low pitch is trans-
mitted with the same efficiency as the 1000
cycles. Then a high frequency of about 5000
cycles is transmitted to check the characteristics
at this end of the frequency range, and if neces-
sary, appropriate adjustments are made. Finally,
music from a phonograph is sent over the circuits
to give a working check on their condition.
The transmission supervisor is also responsible
for the operation of the program circuits during
use. As soon as a report of transmission difficulty
reaches him, he must take immediate steps to
correct it. Whether the trouble is noise on the
circuit or low volume, he must proceed im-
mediately with the proper steps. Sometimes the
volume delivered by a circuit will diminish or
the circuit will become noisy so as to suggest
approaching failure. In this case he endeavors
to obtain an alternative circuit and substitute it;
sometimes this may be done before the radio
listeners realize that any trouble has occurred.
At other times a circuit may, without warning,
fail completely, and at such times the tians-
mission supervisor's general knowledge of the
situation is put to the test. He may sometimes
succeed in obtaining an alternative circuit with
only three or four minutes interruption to tin
program. Sometimes alternative circuits follow
different routes and far exceed in length the
facilities they replace, such as during the Dem-
ocratic Convention in 1924 when a connection
1400 miles long was substituted in place of one
only 200 miles long. The transmission supervisors
even keep informed of the weather conditions
over a large part of the country so that, in case of
threatening storms, they may obtain emergency
routes and hold them in readiness.
The heading shows the program circuit control
point at Chicago. Repeaters, equalizers, oscil-
lators, transmission measuring devices, and other
apparatus, may be seen mounted at the left and
in the rear. One cone is connected to the Red
Network program, another to the Blue Network,
another to the Purple Network (the Columbia
Chain), and the fourth is a spare. In this way,
constant check is kept on the quality of the pro-
gram transmission. At the right are telegraph
operators who transmit messages between the
transmission supervisor and the different re-
peater stations under his direction.
NETWORKS REGULARLY OPERATING
THERE are now four networks in daily opera-
tion, namely, the Red, Blue and Purple net-
works in the East, and the Pacific Coast network
in the West. The eastern networks are supplied
with studio programs from New York City and
the Pacific Coast network from San Francisco.
The total length of program circuits perma-
nently connected into these four networks, or
connected on a regular recurring basis, was, on
April I, more than 15,000 miles. To maintain
and operate this great amount of program facili-
ties required more than 25,000 miles of telegraph
circuit. The daily audiences listening to the pro-
grams from these chains are estimated in the
millions of persons.
Perhaps the reader has wondered how the
designation of networks by colors originated.
This occurred several years ago when the only
network then operating received programs from
WEAF in New York. The telephone engineers
drew in red pencil, on a map, the circuits regu-
larly connected and drew in blue the extensions
which were occasionally added. In this way the
regularly operating chain became known as the
" Red network." Later, when a network was
organized with wjz in New York as the key
station, the name " Blue network" was, of course,
given to this. At the important program control
points the designation of the networks by colors
is a considerable aid to the transmission super-
visor in the necessary switching operations.
HISTORICAL SPECIAL HOOK-UPS
ON DEFENSE Day, September 12, 1924, two-
way conversation between General Pershing
in Washington and the Commanding Generals
of the various • Corps Areas in New York,
Chicago, San Francisco and other points was
transmitted to a number of radio stations and
heard by many thousands of listeners. This
occasion remains an unbroken record for the
broadcasting of two-way conversation.
The largest number of radio stations ever con-
nected was during the Radio Industries Banquet
held in New York on September 21, 1927, when
a total of 85 radio stations broadcast the pro-
ceedings. All four of the regular networks were
used and 13 additional points were added.
Doubtless many readers will recall the first
Dodge Brothers broadcast of January 4, 1928,
when well-known persons in Los Angeles, New
Orleans, New York, Chicago and Detroit were
heard. The circuits used in this broadcast are
shown in heavy lines in the drawing on this page,
totaling over 20,000 miles of circuit, or over
40,000 miles of wire. Other program circuits
operating on this date but not transmitting the
Dodge program bring the total program mileage
to about 24,000 miles of circuit or about 48,000
miles of telephone wire. In addition to this
telephone mileage, about 40,000 miles of tele-
graph circuit was employed for lining-up and
operating the program circuits. As the pick-up
point was changed from one city to another, the
circuits had to be switched at correspondingly
widely separated switching-points. To perform
these operations in the necessary order within
the allotted five seconds required thoiough
training and a high degree of intelligence. All
the pick-up circuits not in use for a few minutes
were kept under continuous test to guard
against the development of line troubles during
these intervals.
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CHAIN BROADCASTING CIRCUITS
OPERATING IN THE UNITED STATES
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AT THE END OF 1927
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IMFW.N AND INTI-.HPHKTATIQN OF rtlHHFNT KADIQ EVFNTX
Broadcasting Needs Capable Leadership
ADIO broadcasting is indeed a healthy
structure to survive successfully the
machinations of the politician, the
cupidity of the direct advertiser, the absence of
articulate listener sentiment and the regulation
of an impotent and hesitant administrative
commission. Only its real service to millions of
listeners gives broadcasting its vitality. On every
hand, radio is the victim of conflicting interests.
The powerful, well-financed broadcaster is as-
sailed for his supremacy by the less capable
station; the vote-seeking politician, with a local
point of view, hampers regulation by those who
understand frequency assignment as a scientific
and national problem; the ethical goodwill
broadcaster is tempted by the example of the
blatant radio advertiser. Only one influence can
lead the way out of this welter of confusion and
that is a crystallized listener sentiment.
In its riotous career, broadcasting has had
many tormentors. Of these, the most disturbing
is the belated and superfluous broadcasting
station which has brought congestion, inter-
ference, and confusion. Throughout its history,
broadcasting has lacked capable independent
leadership to bring it through the wilderness of
uncontrolled growth. It is illuminating to review
the causes of present-day congestion because
they point the way to a solution.
When radio held the center of the stage of
public attention, the number of stations grew
rapidly to the full capacity of the broadcast
band. Room for greater power and more stations
could be gained only at the cost of curtailing
the service of an existing station. Two years ago,
the fight of one station for another's time on the
air upset the Department of Commerce's as-
sumed authority over broadcast regulation,
which was valiantly stemming the rising tide of
stations. An effort was then made to preserve
order by a gentleman's agreement among the
existing stations. But the success of such a
course was unfortunately predicated upon the
requirement that all of those concerned be gentle-
men.
During that period of chaos, broadcasting
stations were erected with reckless abandon and
total disregard of the capacity of the broadcast
band. All broadcasting was conducted in a
bedlam of shrill whistles and sullen groans.
Stern parents punished their children by making
them listen to the radio nightmare. But did a
voice, representative of listener sentiment, arise
in powerful protest? Did any leader of the
industry face the facts squarely? On the con-
trary, the press was flooded with statements
that there was really nothing wrong with the
radio situation.'
After several months of torture, Congress
began to grapple with the situation. But did
anyone come forward with the insistent demand
that the number of radio stations be promptly
and emphatically reduced? The leaders of the
radio industry unremittingly labored to get
some kind of legislation passed. When debate
centered upon two forms of regulation — by a
commission politically subservient to Congress or
by a government bureau reporting to a cabinet
officer and relatively free of political instability —
did the industry declare itself squarely against
political regulation? Indeed it did not; it meekly
favored both bills and, naturally, the bill giving
political influence the greatest sway became the
Radio Act of 1927.
Then came the regime of the Federal Radio
Commission. Did the Commission display the
courageous qualities of leadership essential to
success in its onerous task? Its every act indicates
that internal strife vitiated any constructive
measures. For six months, it dabbled with its
job. Credit must be given for its success in one
respect; the Commission did manage to work
out the best allocation possible without invoking
the only course which would be successful — the
elimination of excess stations in congested dis-
tricts. The Commission talked about strong-arm
methods one day and adopted weak-kneed
policies the next; it announced that it would
eliminate 300 stations from the broadcast
spectrum and then promptly changed its mind.
The progressive members of the Commission
were invariably overruled because they could not
successfully face the political pressure of Con-
gressional overlords who invariably backed the
weak against the strong.
When chivalry is applied to broadcasting, it
means the support of less competent stations
against the so-called chain monopoly. But to
what stations does the listener turn his dials?
ANCIENT TRANSMITTING HISTORY
Parts of the first wireless telegraph installation
in Porto Rico, built for and operated by the
United States Navy. The station was located
near San Juan and was completed in December
1903. The coil is the antenna tuning helix and
below it is the spark gap case. To the left is the
box containing the glass condenser plates. The
spark gap was enclosed in the wooden box be-
cause of the terrific noise produced
68
He selects the powerful stations offering high-
grade programs. As Representative Davis of
Tennessee pointed out, two chain organizations,
operating through seventy-two stations, slightly
more than ten per cent, of the total number of
stations on the air, have 50 per cent, of the total
broadcasting power. The remaining stations on
the air might be classed in two groups: promis-
ing independents, offering high-grade programs
and worthy of expansion, and the small, advertis-
ing and propaganda stations, which now stifle
the growth of the better independents. The pre-
dominance of the chain stations is founded en-
tirely upon the crowding of the more worthy
independent stations by the host of worthless
ether busybodies. The elimination of 300 small
stations, particularly in large cities where power-
ful locals exist, would give a well-balanced struc-
ture of chain and independent stations.
In all the vast amount of conversation pre-
cluding the passage of the amendment demanding
equalization of broadcasting, no one succinctly
and forcefully stated the position of the broad-
cast listener. The villification of the leading
stations on the air went unchallenged. The
equalization amendment is a farcical grandstand
play, which glibly overlooks the fundamental
causes of concentration of stations in the more
populous areas. Merely to declare the sound
principle that broadcasting shall be geo-
graphically equalized will not create the needed
stations in the sparsely populated areas or the
necessary channels so that they might operate.
To equalize the power in the five zones, only
three possible courses exist :
(i) Power in the weaker zones may be
increased so that it equals that in the more
progressive zones; (2) power in the strong
zones may be reduced to the level of the
weaker; or, (3) a middle course between these
two extremes may be adopted.
Commissioner Caldwell showed that to bring
up the power of the weaker zones to that of the
highest would require the addition of 276
stations with 460,000 watts power. Inasmuch
as the broadcasting band is already hopelessly
overcrowded, any such increase, in fact any in-
crease at all, would bring nothing less than
chaos. Averaging the present total power among
the zones would require a power cut in the first
zone of 92,000 watts, curtailing the service of the
most valuable stations on the air. At the same
time, there are no stations in the South ready to
bring that section up to average. Reducing the
power of all districts to that available in the
weakest would be wholesale destruction of good
broadcasting.
The broadcasting industry should be en-
couraged to erect more great stations; the better
independents should be given the opportunity
to serve, unmarred by the excessive number of
weaklings on the air. Unless the Commission
develops an unlooked-for independence and
courage, it will respond to the temper of Congress
by hampering the growth of bigger and better
stations. What we need is more, and not less,
powerful stations in every section of the country.
Only if listener sentiment becomes suddenly and
JUNE, 1918
BRITAIN WANTS PROOF OF TELEVISION
69
Present Distribution of Broadcast Stations
THE following is an analysis of broadcasting
stations licensed as of February 29, showing
the inequitable distribution of stations by zones.
Commissioner Sykes, representing the south-
ern zone, has pointed out that every legitimate
request for power increase and improved chan-
nels, made by southern stations, has been
granted and that the inequalities are due rather
to lack of progressiveness with respect to broad-
casting in the South than to any discrimination.
POPL LAITON
POPI> ARE*
[ ATION (square
\ftrcrnl.) milts')
AREA NUMBER TOTAL
(ptr OF STA- STATION
»Y»/.) TIONS VOWfiR IN
WATT*
PER-
CENTAGE
OF STA-
TION
POWER
STA-
TIONS
WITH
OVER
IOOO
WATTS
ZotK
(New England
Sts. N. 1'. &
24,378,13'
22.73
1 29.769
363 138
21.3,055
3530 10
N. J.)
Zone 2
(Central West &
Middle Atlantic)
24,337. MI
22.69
247017
h 93 1 1 5
116,805
19.34 8
(Southern)
24,826,050
23.14
761.895
21 33 102
47,105
7.80 4
7one A
(Northwest)
24,492.986
22.83
658.148
1*42 215
164,870
27.31 30
Zone s
Western &
Pacific Coast)
9.2 li, 720
8.59
1.774.447
4.1 h8 Hi
61.785
.10,2^ 8
TOTAL
l07.248.JiS
100
3.571.776
IOO TO I
603.620
100 60
immediately articulate, and a powerful sweep of
opinion champions the two or three hundred
favorite stations, can the destructive effects of
the selfish and uninformed propaganda of
Congress against good broadcasting be overcome.
Mergers in the Radio Industry
THE proposed merger of the Radio Cor-
poration and the Victor Talking Machine
Company would be a vital step in bringing
us that combined broadcast receiver, phono-
graph, home motion-picture projector and tele-
vision receiver which wej forecast in these edi-
torials for January, 1928, as the ultimate home
entertainment machine. The total assets of the
Victor Company are about sixty million dollars;
those of the Radio Corporation about sixty-five
million dollars. The merger will make available
to thj combination the services of renowned
artists, both for radio purposes and for talking
movies. The announcement that negotiations
for this merger were under way was greeted with
the usual monopoly accusations in Congress.
Unquestionably the merger would result in a
still stronger company. The consolidation of
these interests is, however, certain to enhance
the entertainment value of broadcasting and
hasten the further development of diverse visual
and tonal amusement in the home.
Another merger of vital importance to the
American radio industry is the combination of
the Marconi Wireless Telegraph Company of
England with the Eastern Telegraph Company.
This forms a one-hundred-million-dollar, world-
wide communication corporation which may
impose the pressure of severe competition
upon the Radio Corporation of America. In
spite of the comparative youth of the Radio Cor-
ooration, it has become a sufficiently vital factor
in international communications to make this
consolidation of British communications neces-
sary.
A third merger which will ultimately affect the
radio communication business is that of the
International Telephone & Telegraph Company
A'ith the Mackay interests. The former controls
telephone properties in Cuba, Spain, and South
America and has exclusive rights for foreign
manufacture of Western Electric Company prod-
ucts. The Mackay interests have an ambition to
set up an international radio telegraph network
and may ultimately become serious rivals to the
Radio Corporation of America. The Mackay
radio patent rights are based on their acquisition
of the Federal Telegraph Company and Federal"
Brandes.
More High Power Broadcasting
IT IS understood that the Crosley Radio Cor-
poration, operating WLW, has applied for a
50,ooo-watt assignment and that, like-
wise, KFI in Los Angeles is to have a similar in-
crease. The only southern station to seek a
substantial power increase is KWKH. It is un-
fortunate that some of the more reputable
broadcasting stations in the South are not
aiming at substantial power increases, because
there are many good reasons why KWKH in
particular should not be favored by the Federal
Radio Commission. This station, in plain de-
fiance of the Commission, increased its power
surreptitiously and utilized its facilities for
Nullification of members of the Commission. It
has established little reputation for high-grade
programs, although it is by no means at the bot-
tom of the list in that respect. We regret to see
this progressiveness for much needed sub-
stantial power increases in the South largely
confined to a station which has virtually
thumbed its nose at the Federal Radio Commfs-
sion and defied the simplest precepts of law and
order.
British Skeptical of Baird Tele-
vision Accomplishments
A PUBLICITY statement from the Baird
company says that a picture of Miss
Dora Selvey, transmitted by Baird tele-
vision from London to the Berengaria, a thou-
sand miles at sea, was considered recognizable
by the radio operator. It must be realized that
any kind of a radio transmission, which is in-
terpreted by any form of television machine,
makes some kind of impressions on the screen.
The photographs of long distance television
reception, published in the newspapers, which
we have examined, have all been faked, the
image drawn on the screen being the work of
a retoucher. Newspapers, with a nose for news,
however, do not hesitate to fool the public.
Popular Wireless, a British home constructor's
magazine, offers to pay Mr. Baird £1000. if he
will successfully televise by radio, over a dis-
tance of not less than twenty-five yards, certain
items such as a series of three recognizable faces,
five simple solid geometric models in slow mo-
tion, four animal toys, grouped and in slow mo-
tion, and a tray, containing dice and marbles to a
number not exceeding twelve, all of these objects
to be sufficiently clear that a committee of judges
can recognize them and state their number. The
same publication points out that the television
sets being marketed in England, which are not
true television but shadowgraph machines,
require a high voltage supply of six or seven
hundred volts, which is quite capable of giving a
fatal shock.
Dr. Herbert E. Ives of the Bell Laboratories,
who demonstrated the first television appara-
tus between Washington and New York in
April, 1927, stated recently that bringing into the
home by radio an actual spectacle like a great
athletic event is unthinkable because its cost
would be simply enormous. Television is most
effectively accomplished through wire lines
and displayed in theatres and auditoriums
so that large numbers of people will divide the
cost of the presentation.
WHEN the S. S. Robert E. Lee ran on the
rocks while en route from Boston to New
York on March Q, several broadcasting stations,
tending to interfere with the handling of SOS
traffic, were very slow in getting off the air.
Among the stations named by the Federal
Radio Supervisor, were wjz, WRNY, and wot.
© Harris & Ening
THE FEDERAL RADIO COMMISSION IS COMPLETE
After long delay, the vacancy on the Commission was filled by the President and all the members
confirmed by the Senate. From lelt to right.- Sam Pickard, O. H. Caldwell. Carl H. Butman (secretary).
I o Sykes^ H. A. Lafount, and I. E. Robinson, chairman
70
RADIO BROADCAST
JUNE, 1928
Laxity in this respect is rarely displayed by the
more important stations and the lesser, having
high-frequency assignments, are least likely to
cause dangerous interference. Since it may be a
matter of life and death, leniency to those who
fail persistently to shut down promptly for dis-
tress traffic should hardly be tolerated. The
violations so far noted have been only spasmodic
and quite accidental.
Here and There
THE Public Health Service broadcasts, which
were begun in 1924, are now being used
semi-monthly by fifty-four stations. 310 radio
lectures have so far been delivered.
ASA result of the forty per cent, reduction
*• in transatlantic telephone rates, there has
been a fifty per cent, increase in the number of
calls handled.
\ A /CDA, a broadcasting station licensed in
* the New York area, for some mysterious
reason, after the Federal Radio Commission
went into operation, has sued WOR for $100,000.
for an alleged harmonic, attributed to WOR,
which causes heterodyne interference with its
programs. WOR'S frequency is 710 and that of
WCDA 1420. As a matter of fact, two predominant
heterodynes assail WCDA'S carrier, both of which
cannot be attributed to WOR. The technical
standards, maintained by WOR, are beyond ques-
tion and whatever radiation there may be on
its harmonics, are certainly suppressed to the
minimum which the present standards of the
radio art permit. Should WCDA'S pretentious suit
be successful, it would inevitably lead to other
suits because harmonics cannot yet be entirely
avoided. The second harmonic of all stations,
having a fundamental frequency lower than 750
kilocycles, falls in the high frequency end of the
broadcast band. The successful prosecution of
WCDA'S suit would place in jeopardy all the
broadcasting stations which are assigned to fre-
quencies below 750 kc. WCDA should never have
been given a license in the first place.
THE SET BUILDER IN DETROIT
CARLY in April, manufacturers of radio
*~* parts and accessories exhibited at Conven-
tion Hall in Detroit, featuring the newest a. c.
developments, units for the use of custom-set
builders, equipment for converting battery sets
to a. c., parts for improvement of receiving sets
now in use. The large attendance is indication of
the power and numbers of the knights of the
soldering iron.
A JOBBER section has been formed by the
** Federal Radio Trade Association. The
manufacturers' relation committee of the
section is headed by Harry Alter, the member-
ship committee by J. M. Connell.
RADIO SALES IN FIGURES
THE average business done by radio jobbers
is $218,000 annually, according to figures
from a survey made by the Electrical Equipment
Division of the Department of Commerce and
the National Electrical Manufacturers' Associa-
tion. Three hundred and seventy-five jobbers in
New York, New Jersey and Philadelphia did an
average volume of $298,000; the New England
group $264,000; Great Lakes region $240,000
and southern states $1 18,000.
Small-town radio dealers, according to a survey
by the same Bureau, average $5200 a year, as
compared with $22,800 by the average New York
dealers. The Philadelphia average was $21,000;
Chicago $32,200. A group of cities, including
Boston, Baltimore, Cleveland, Detroit and St.
Louis, show an average of $44,300.
Radio Retailing estimates the sales of radio
sets in 1926 at $506,000,000 and in 1927 at
$446,550,000. Radio is now installed in 27 per
cent, of American homes. If broadcasting condi-
tions are not soon improved, radio set sales
will continue to decline.
NO NEW IDEAS IN PROGRAMS
COMMENTING editorially on commercial
^"* broadcasting, Editor fir Publisher states:
"The rare incidence of new ideas in the program
departments of large radio studios is beginning to
worry the men assigned to the development of
new converts in broadcasting. The monotony is
beginning to pall on its makers and the feeling
is expressed that the pall may extend to the pay-
roll unless expert direction is found to steer pro-
grams into new channels. ... As a rule, the radio
program staffs are competent to provide a well-
balanced evening of entertainment. They know
nothing of selling merchandise and the applica-
tion of advertising to the development of sales.
They have constructed a program and stuck
into it, like splinters into a fruit cake, occasional
mention of the sponsor's name and goods. The
advertising interludes to the entertainment have,
in recent weeks, become more and more blatant."
Editor fir Publisher's charges are, in the main,
true. There have been very few instances of
originality in the form of program presentation
during the last few years. One answer may lie
in the fact that successful moving picture
directors get from fifty thousand to two hundred
thousand dollars a year, while the number of
program directors in the radio field who make
more than five thousand dollars a yea an be
counted on the fingers of two hands.
PENDING SHORT-WAVE APPLICATIONS
/^\NE hundred and fifty applications for short-
*-J wave channels by new commercial and
public short-wave stations, requiring 350 chan-
nel assignments, are now pending before the
Federal Radio Commission. Communication
companies are making 45 applications for 137
channels; newspapers 31 for 97 channels; oil
companies 28 for 29 channels; brokerage houses
12 for 22; steamship companies 7 applications
for 13 channels; banking houses 6 applications
for 6 channels; motion picture producers 5 ap-
plications for 10 channels; rubber companies 3
for 4 channels; coal i application for 2 channels;
automobile and transportation companies I
application for i channel; and miscellaneous
businesses 5 applications for 7 channels.
If these assignments are granted and the
channels placed in use, the rivals of these com-
panies will also want channels and, since further
channels will not be available, the Federal
Radio Commission will, of course, be charged
with discrimination. The principle of first come,
first served, which must apply when a limited
number of any commodity is being dispensed,
always carries in its wake the cry of discrimina-
tion.
NEW AMATEUR BANDS
r* ENERAL order No. 24, by the Federal
^-* Radio Commission, opens the 2o,ooo-to
3O,ooo-kc. band to the amateur. The assignments
are now as follows:
64,000 — 56,000 kc. 4.69 — 5.35 meters
3,550 — 3,500 kc. 84.5 — 85.7 meters
2,000 — 17.5 kc. 150 — 175 meters
A SHORT-WAVE radio picture receiver,
** installed on the Hamburg American liner
Resolute, is said to be successful. Small pictures
and letters can be sent for moderate distances
at a cost of one dollar.
THE NEW G. E. HIGH-FREQUENCY TUBE
DR. W. R. WHITNEY of the General
Electric Company recently described a
new high power, high frequency, short-wave
tube, generating fifty million cycles. It radiates
ten to fifteen kilowatts. Interesting psychological
effects have been noted, particularly a warming
RADIO BRIGHTENS THE LIFE OF OHIO RIVER FOLK
House-boat dwellers along the Kentucky shore of the Ohio River. The receiver is pulling in WGY and
is the first radio reception these folk have ever heard. The set was an important part of the equipment
of Lewis R. Freeman, member of the Explorers' Club of New York who traveled from Pittsburgh to
Cairo — a distance of 1000 miles along the Ohio River. This set was used to bring in weather forecasts
while navigating the river and in one case, at Louisville, picked up a cyclone warning, enabling Mr.
Freeman to avoid a tornado that might have destroyed his expedition
JUNE, 1928
NEWS OF RADIO EVERYWHERE
71
effect on the blood of persons within its influence.
Small arcs are readily established by metallic
conductors. Eggs and sausages have been fried
by the heat generated on a single wire.
NEW RADIO AVIATION BEACON
"THE visual indicator, developed by the
*• Bureau of Standards of the Department of
Commerce, to show the aviator his course,
employs a needle-like reed, moved by electrical
impulses received from the radio beacon It
does away with headphones and trailing antenna.
It works on the familiar balanced signal principle
and gives indications for distances of fifty
miles. In mountainous regions, however, its
directional accuracy varies 'but the device should
be of inestimable help in locating a landing field
through a fog when the aviator is not far distant
from the field. Guided by the beacon, he can
come within range of the fog-penetrating neon
light and thus make a successful landing which
might not be possible without the radio direction
finder.
QWEN D. YOUNG flatly stated recently that
the British lead America in international
cable and radio communication. "The English
Government," said Mr. Young, "fearing pre-
domination of the American radio group in the
world of communication, has practically coerced
the interests in England to combine cables
with radio in order that the English domination
of cables may continue. In America. Congress
has enacted directly a piece of legislation stip-
ulating that there can be no cooperation or
relation between the cables and radio. Congress
had distintegrated our strength into small units
and put each one of them at the mercy of a large
centralized foreign group."
/^OVERNMENT officials in Czechoslovakia
^J estimate that the saturation point in the
possible number of receiving set owners has
been reached in that country unless more broad-
casting stations are erected. There are now
206,000 listeners in Czecho-Slovakia which has a
population of some thirteen million.
D UMORS have appeared in the press that
1V several large holders of R. C. A. licenses
have stopped payment on their license contracts
and served notice to the effect that at the
present time they are not able to carry out their
agreements because of heavy declines in sales
and the inability to realize on large stocks of
battery sets.
"THE Brunswick Phonograph Company an-
' nounced that it will place records of certain
commercial broadcast programs on the market
the day following their presentation. It's bad
enough to hear most radio programs but once1
BRITISH SHORT-WAVE EXPERIMENTS
H characteristic caution, the British
broadcasting monopoly announces, through
its Chief Engineer, Captain Eckersley, that
the 5 sw high-frequency transmissions arc
being attempted largely to permit foreign and
dominion experts to ascertain field strength on
various frequencies. "It would be criminal fool-
ishness," says the announcement, "to let these
encourage one into saying that there is yet a
guarantee of satisfactory service worthy of the
object served."
International broadcasting, through short-
wave interconnecting links, is still a spectacular
demonstration with all the hazards of uncer-
tainty. But any new art must begin in this way
and the experiment should he encouraged. Its
success will accomplish much more than all the
peace conferences and pacifist disarmament
propaganda.
BROADCAST AREA SERVED IN AUSTRALIA
"THE interests operating station 3 to in Mel-
1 bourne, Australia, have shown, by super-
imposing a map of Europe upon that of Aus-
tralia, that six Australian broadcasting stations,
all fringing the coast, serve an area equal to
that of Europe, including Great Britain and Ire-
land. Most of the population of Australia, how-
ever, is distributed in centers along the seacoast.
There is no problem of frequency shortage to
hamper the increase of broadcasting stations, but
it appears that the government authorities
hesitate to permit an increase in the number of
broadcasting stations.
BROADCAST COOPERATION IN EUROPE
'THE Union International de_ Radiophonie,
I which consists of delegates fium all Euro-
pean countries operating broadcasting stations,
is concerning itself with such problems as
frequency assignments, accurate frequency
measurements and the formulation of the fre-
quency requirements of the various nations.
This body serves the same function as the
Federal Radio Commission in the United
States, except that it has no 'legal authority
and must settle its affairs by mutual agreement
and conference.
pCJJ, the Dutch short-wave broadcasting
station, frequently heard by American
enthusiasts, has adopted a schedule as follows:
Tuesdays and Thursdays, 16 to 19 Greenwich
mean time, and Saturdays 14 to 17 G. M. T.
A USTRIA now claims to be the most pro-
gressive country in the broadcasting field,
so far as percentage of registered listeners is con-
cerned. 300,000 out of its 6,500,000 population
are registered radio listeners. Radio manufactur-
ing is also developing rapidly, exports being
four times greater than imports.
FACSIMILE TRANSMISSION USED
THE extent to which financial enterprise is
1 utilizing the modern means of electrical
communication is illustrated by the recent float-
ing of ten million dollars in bonds for Warsaw,
Poland, simultaneously in Europe and America.
A 1400-word descriptive circular was compiled
and sent by radio to London and Stockholm.
Quarter-page ads were then set up. in London
and mats made and distributed by air mail to
other European capitals. The circular was
cabled to South America and put into type. In
New York, it was set up and distributed by
telephoto to cities as far west as the Pacific
Coast. Thus transatlantic radio picture circuits,
airplanes, telephoto, and cable were used in this
international financial venture.
THE transatlantic telephone service was ex-
tended to Belgium on January 19 and to Holland
on January 30.
HERBERT H. FROST, formerly General Sales
Manager of E. T. Cunningham, Incorporated,
has resigned to become Vice-President of Federal-
Brandes, Incorporated.
D ADIO beacon service is to be installed along
I v the French coast. One station is to be built
at the mouth of Cherbourg harbor and another
ten miles northeast of that point so that bear-
ings can be given to incoming ships.
A DECISION of the U. S. District Court in
Cincinnati declares that the Crosley Musi-
cone does not infringe upon the Lektophone
patents. The Musicone, says the decision, is
drawn from the same prior art that the Hopkins
invention is made and is an improvement thereof.
The Supreme Court of Canada holds that the
patent granted by the United States to the
German inventors Schoelmich and Von Bronk
is prior art over the Alexanderson tuned radio
frequency patent. This is directly opposite to
the opinions of American courts.
— F. H. F.
RADIO CABIN OF THE MOTORSHIP "BERMUDA"
This is the latest type Marconi installation for ships and shows (left to right) gvro-compass repeater
•Ltion finder; receiver operatmg on all wavelengths from 300-20,000 meters 'kwo ctad
spark transrm.ter; ,1-kw. c.w. and i.c.w. tube transmitter working between f^ ami 2^.0 meters
By LEROY S. HUBBELL
IF WE review the development of the me-
chanics of a radio receiving set we remember
a panel resembling a small switchboard
which had primary and secondary inductance
switches, an A battery control switch, several
variable condenser controls and other minor con-
trol switches. Gradually, over several years,
these numerous controls began to disappear
until now, on the panels of many of the recent
designs, not more than three controls exist,
namely, the on-off switch, a single dial for con-
trolling the variable condensers, and sometimes
a volume control.
While there have been many improvements
toward simplifying the tuning of a radio receiver,
it is still necessary to manipulate a dial and if
a particular station is desired it is necessary
to consult a schedule. If no tuning schedule is
available the settings are oftentimes haphazard.
In a large number of cases, particularly in the
metropolitan areas, the dial settings are usually
confined to not more than five to ten stations.
When one is comfortably seated, whether in a
favorite armchair by the fireside or at the table
enjoying a dinner or participating in a card
game it is annoying to interrupt one's activity to
adjust the radio to some other station in search
of a more delectable program. The partial elimi-
nation of the multi-controls on the radio receiver
has reduced immensely the trials and tribulations
of many a lover of radio entertainment. Probably
there will always be at least two controls, one
for the station setting and another for the volume
from the loud speaker. Take these two controls
to the armchair by the fireside or to the table and
the ideal radio entertainment is at hand.
In this article we discuss a means for auto-
matically tuning a radio receiver at a remote
point, although the same equipment may be
used in connection with a transmitting station
where the tuning elements are adjustable. The
advantages may be summarized as follows.
1. The set may be tuned to any one of
several definite stations by pressing a button.
2. The set may be controlled at any point
of convenience.
}. The radio receiver may be housed in a
closet or other out-of-way place reducing
considerably the cost of expensive furniture.
4. An outdoor directional loop type an-
tenna may be used instead of the present
antenna.
[Judged by present standards, Mr. HubbelPs
automatic tuning mechanism has certain draw-
backs, as well as obvious advantages. These
limitations hold for all automatic tuning me-
chanisms with which we are familiar. The appar-
atus takes up considerable space, and although,
as Mr. Hubbell suggests, the receiver and the
tuning mechanism may be located elsewhere
than in the living room or the den — or wherever
receivers now in common use are located — it is
necessary to place the automatic mechanism
quite close to the radio apparatus and in most
cases that involves rearranging at least the radio
frequency and detector circuits of the receiver.
Neither Mr. Hubbell's arrangement or any other
can readily be applied to the average existing
receiver. That is, of course, not a serious disad-
vantage, for it is not difficult to rearrange a
"pet circuit" so that the relay tuning controls
are operative. Cost, too, is a factor, but a very
real gain in convenience is achieved which should
equalize that. — Editor.]
AN EXPERIMENTAL SET-UP OF THE HUBBELL AUTOMATIC TUNING CONTROL
The photograph shows a rough model of the tuning control apparatus and the radio and detector circuits
of the receiver. The motor in this illustration is much larger than necessary. The model shown is equipped
for tuning only to one broadcast station. For each additional station, two more cams, one on each shaft
will be required and one additional relay for each station
THE APPARATUS USED
THE equipment designed by the author for
automatically tuning radio apparatus con-
sists essentially of a small commercial type motor
of about 6>0- h.p. or less, depending on the num-
ber of stations the equipment must tune to,
connected to a revolving iron disc through a re-
duction gear. The revolving iron disc is caused to
engage at right angles another iron disc by means
of an electro-magnet (magnetic clutch). The
second disc is connected to a series of cams to
which spring contacts engage. Two cams, one
acting as a vernier to the other and a relay are
OF LATE there has been a considerable interest
in the automatic tuning of radio receivers.
Remote tuning control of radio transmitters has
been used for some time, in various forms by both
commercial and military radio stations, but until
recently, little bad been done to explore the possibil-
ities in the radio receiver. This timely article by
Mr. Hubbell describes the mechanical principles
of the system which he has devised; the illustrations
show a rough model. A commercial model would
probably be quite different in arrangement and
appearance. Practically, the device suggested by
Mr. Hubbell is limited to the control of from ten to
fifteen stations, but it does permit the manual con-
trol of the receiver at any time. No effort has been
made to treat this subject from the constructional
point of view. Our readers will nevertheless be in-
terested in the description of the present method.
All patent rights are reserved by the author.
— THE EDITOR.
required for each wavelength setting. If the radio
apparatus has more than one variable control
the clutch and cams are duplicated, but the
motor and reduction gear are common to any
number of controls.
At a distance from the radio set there is a
small button box which contains a button for
each wavelength and associated with each button
is a small display lamp to indicate the station
to which the set is tuned. The button box also
contains a rheostat or potentiometer for con-
trolling the volume at the loud speaker.
Except for the push buttons, display lamps
and volume control switch, the tuning mechan-
ism may be housed within the radio cabinet.
For those who are not interested in distant
stations and confine their entertainment to local
broadcast programs it would be practical and
desirable to place the radio equipment in a
closet or other out-of-sight place thus reducing
the cost of the receiver.
In the accompanying Fig. i is shown the
fundamentals underlying the operation of the
automatic tuning equipment designed by the
author. In the lower left hand side of tht- draw-
ing is shown a revolving iron disc, Dj. whose
shaft is connected ' to a small motor (not
shown) through a reduction gear. When the
motor is energized, the iron disc to which it is
connected revolves at about 60 revolutions per
minute. Adjacent to this disc is another iron
disc, D«, the axis of which is at right angles to
the former. These two discs have about //' clear-
ance between their edges. There is a magnet,
Mi, mounted closely against the driving disc,
but not touching it, with one of its poles facing
the driven disc. There is a return pole piece on
JUNE, 1928
AUTOMATIC TUNING FOR THE RADIO RECEIVER
73
the magnet to concentrate the flux at the driven
disc end. On the driven disc there is mounted a
six-fingered suspension spring which connects at
its center the shaft, S, to the driven disc at the
extremities of the fingers. This spring permits
the driven disc to hold up against the driving
disc when the magnet is energized.
On the shaft, S, a cam is mounted consisting of
copper punchings riveted to a fiber disc. The
front of the cam is shown in perspective while
the rear of the same cam is shown at the right
of the drawing in full view. On the front of the
cam it will be noted that the copper punchings
are cut so that the brushes resting against the
cam pass over segments and interrupt any
current which may be passing through the
brushes. On the rear of the cam there are no
breaks in the copper punchings. These copper
punchings are electrically connected to the
punchings on the front of the cam by rivets. In
the upper portion of the drawing a conventional
relay is shown. In the lower right hand side a
push button and a display lamp is indicated.
The shaft, S, is connected to the proper variable
tuning element of the radio set such as a variable
condenser, a variometer, etc.
TUNING FOR STATIONS
BY PRESSING the push button a circuit is
closed beginning with the ground side of the
battery through the contacts of the push button,
and the relay to battery. The relay operates and
in so doing establishes a circuit to lock itself up.
The circuit is as follows: beginning with ground
at the left of the relay through the making con-
tacts to the upper spring pressing against the rear
of the cam, through the rivets of the cam to the
upper brush on the front of the cam back to the
right hand contact spring of the relay, through
the winding of the relay to battery.
At the same time that ground is connected to
the upper brush on the front of the cam. a
ground is placed on the middle brush which
operates the magnet. Also a ground is supplied
to the motor lead which operates a relay in the
motor circuit causing the motor to rotate. The
shaft. S, now rotates and continues to rotate
until the top and middle brush fall into the
open-shaded segment of the cam. The set
screw, A on the cam huh permits the cam to
be set at any angular adjustment so that the
variable element in the radio set can be rotated
to any predetermined selling. In practice there is
another shaft, S» (see the accompanying illus-
trations) paralleling the shaft, S, on which is
mounted a similar cam and brushes. The second
shaft is connected to shaft S, through a gear,
reducing the speed from 60 r.p.m. to 3 r.p.m.
The brushes of the second cam are connected
in multiple with the brushes shown so that by
connecting the variable condenser or other
variable element to the second shaft, a micro-
meter adjustment is obtainable.
When the cam on shaft S has arrived at the
break in the copper punching the circuit to the
motor, clutch and relay is opened. A contact is
made however on the lower brush at both sides
of the cam which completes a circuit from the
ground at the relay (the relay now being re-
leased) through the lower brushes on both the
front and rear of the cam through the display
lamp to battery. The display lamp is lighted to
indicate that the variable element in the radio
receiver is tuned to a wavelength as predeter-
mined by the adjustment of the cam on shaft S.
It should be noted that the lead marked "To
battery switch" is connected to battery through
the released contacts of the relay. With this ar-
rangement all undesirable noises in the loud
speaker are eliminated when the variable ele-
ments are passing over unwanted stations. As
A SIDE VIEW OF THE EXPERIMENTAL UNIT
This illustration shows the mechanical relation of the reduction pulley and the main shaft, Sj
soon as the cam has arrived at its predetermined
station setting the relay releases and through its
contacts supplies current over lead "To battery
switch" to the A battery rheostat
The push button and display lamp indicated
in the drawing together with a plurality of push
buttons and lamps are mounted in a button box
away from the tuning equipment, the latter as
suggested above are housed within the radio
cabinet. From the push button box there are
two wires for each button, a pair for the two
poles of the battery and a lead for controlling
the volume at the loud speaker. For a six-station
controlled set, there would be about 15 wires in
a flexible silk covered cable leading from the
position of the button box to the radio set.
The relays used are of commercial manufac-
ture having resistances of approximately 200
ohms and operating on 6 volts. The magnet is
part of the construction of the tuning mechanism
and is wound to operate on a 6-volt battery at
about 15 watts. The battery used may be either
a loo-ampere storage battery or may be replaced
by an a.c. rectifier which would operate only
when required. Low voltage a.c. for operating
the relay and lighting the display lamp would
also be required if the storage battery is elimin-
ated.
In the photographs, the relays referred to and
the magnetic clutch are marked. The motor,
which rotates at about 1750 r.p.m. is connected
to the device by means of a belt. Between the
motor shaft and the driving disc shaft the speed
is reduced to about 60 r.p.m. through the pulleys
on both the motor and the device and the re-
duction gears on the device itself. The mag-
netic clutch being energized by the relay as
mentioned above, is holding the driven disc
up against the driving disc causing the cam on
To Motor •»
To Battery Switch
Battery
or
A.C. Rectifier
the left hand shaft to revolve clockwise and the
cam on the opposite shaft to revolve counter
clockwise.
The cam on the left hand shaft revolves at
about 60 r.p.m. while the cam on the right hand
revolves about 3 r.p.m. the reduction taking place
through the gears connecting the two shafts.
1 1 will be noted that the tuning device and the
variable condensers are not directly connected.
The means shown permits a free movement of
the condensers through nearly 360 degrees. By
this feature it is possible to tune the radio set
manually to any desired station free of the auto-
matic tuning device. The experimental model is
equipped to tune-in automatically only one
broadcast station, that station being dependent
upon the settings of the two cams. For each
additional station two more cams, one on each
shaft will be required. One additional relay will
also be required for each additional station. The
practical limit is probably about 10 or 15
stations.
For cases where there is another adjustable
tuning element in the radio set and which can
not be directly connected to a single control, it
is possible to tune automatically that element
independently. To do this a shaft is extended to
another device which is similar to that shown.
In this case, however, the only parts which re-
quire duplication are the cams and magnetic
clutch and the spur gears which connect the
upper shaft to the driving disc shaft.
The second relay shown in the photographs is
connected between the push button relay (shown
in diagramatic form in Fig. i) and the motor.
The use of this relay merely separates the direct
current circuit used to operate the radio set
trom the i lo-volt alternating current lighting
circuit which is used to operate the motor.
FIG. I
Schematic diagram
of a method for Ma8"et
automatic tuning I" 1
control of a radio re-
ceiver. The parts
labeled are referred
to in the text
Rivets connecting
oth sides of Cam
Disc suspended
suspension spri
toShaft"S" Pash/
Rear view
'of Cam
Display Lamp
Through Battery Switch
"-Shaft connected to Motor
or other driving power through
Reduction Gear
THE NEWEST POWER TUBE
By Howard E. Rhodes
Radio Broadcast Laboratory
PLATE
VOLTAGE
THH UX-2JO (cx-j5o) "special purpose"
tube is the newest and probably the last
of the line of power amplifier tubes de-
signed for use with radio receivers, for according
to its designers, the power output is about as
large as may be obtained from a tube mounted
in a standard receiving tube base. The glass
bulb enclosing this tube, which determines the
amount of heat that can be dissipated, is as
large as is feasible using this base.
To what use can this power tube be put? What
advantages and disadvantages has it over other
types? Let us compare it with others to get a
clear picture of the relation between the 250
and other tubes.
Fig. I shows how the power output of this
tube compares with that of the other types of
power tubes at various plate voltages.
TABLE I
UNDISTORTED POWER OUTPUT IN MILLI-
WATTS
112 171 210 250
90 40 130
135 120 330
157 195 500 90
180 700 140
250 340 900
350 925 2350
400 1320 3250
450 1760 4650
The figures in Table I together with data on
several push-pull combinations have been
plotted in Fig. i. This graphic representation
of the power output of various tubes and com-
binations of tubes, as a function of plate volt-
age, serves well to illustrate the relative position
of each tube from the standpoint of power out-
put.
When interpreting these curves, it should be
appreciated that a considerable increase of power
output is necessary in order to make the effect
appreciable to the ear. Twice the power output is
equivalent to an increase of 3 TU which is not
very great, i TU being a just audible increase.
It is necessary that the available power be in-
creased two or three times in order for the in-
crease to be worth while.
The choice of which type of tube is used de-
pends, obviously upon how much power output
is desired. If not more than 200 milliwatts are
required, the 1 12 may be used ; for a power output
up to 700 milliwatts the 171 type tube is used.
If greater power than this is required we can use
either a 210 or a 250 type tube. A more detailed
analysis of these two tubes, showing how their
power output varies with the applied plate volt-
age is given below.
POWER OUTPUT OF 210 TUBE
PLATE POWER PLATE GRID
VOLTAGE OUTPUT CURRENT BIAS
(Milliwatts) (mA) (volts)
250 340 10 18
350 340 16 27
450 1700 18 39
POWER OUTPUT OF 250 TUBE
PLATE POWER PLATE GRID
VOLTAGE OUTPUT CURRENT BIAS
(Milliwatts) (mA) (volts)
250 900 28 45
350 2350 45 63
450 . 4650 55 84
This table is very interesting for it shows that
at all plate voltages, the 250 tube is capable of
delivering more than twice the power output of a
210 tube. For use in a straight amplifier (not
push-pull) the tube, from the analysis given
above, seems to be much the best for it is capable
of delivering much more power than any other
type of tube. When operated at maximum volt-
age, the 250 can deliver a power output of 4.6
watts which is about as much as can be obtained
from two 210 type tubes in push-pull. In the
following paragraphs a more complete compari-
son is given of a single 2501'$. 2io's in push-pull.
POWER SUPPLY EQUIPMENT
A BOUT 450 volts are required in both cases
** and the plate current requirements (about
40 mA. for 2io's in push-pull and 55 mA. for a
single 250) are not sufficiently different to make
the power supply equipment much cheaper for
one of the two arrangements. In so far as the
power supply is concerned, therefore, there is no
distinct advantage in favor of a single 250 rather
than two 2io's in push-pull or vice versa.
A COMPARISON OF COST
SINCE ordinary transformers are cheaper
than push-pull transformers it is somewhat
less expensive to construct a power amplifier
using a single 250 type tube than two 2io's in
push-pull. For example, suppose that trans-
formers costing about as much as Amertran's
were to be used in the amplifier,
SINGLE 250 TUBE
Input transformer $10.00
Output device 10.00
One 250 type tube 12.00
One socket 1.00
Total . $33.00
210'S IN PUSH-PULL
Input transformer
Output transformer
Two 210 type tubes
Two sockets
Total
$15.00
15.00
18.00
2.00
$50.00
FIG. I
How the power output of the 250 type power
tube compares with other types of power tubes,
at various plate voltages
74
Here we see a distinct advantage in favor of
a power amplifier using a single 250 tube and
delivering to the load about as much power as
2io's in push-pull, which will cost only about
65 per cent, as much as a push-pull amplifier.
A COMPARISON OF QUALITY
IN THIS characteristic, the push-pull arrange-
' ment is theoretically better than the single
tube because the former arrangement eliminates
second harmonic currents — currents which rep-
resent distortion and which are passed on to
the loud speaker when only a single tube is used.
However, even with a single low-plate-im-
pedance tube such as the 250, there isn't much
second harmonic current generated by the tube
in the load circuit when the tube is delivering
its rated power, or less for under the condition
that the tube is working into a load impedance
approximately twice as great as the tube's plate
impedance the amount of second harmonic
current in the output is not greater than 5 per
cent. — an amount of distortion which is con-
sidered small enough not to be appreciable to
the ear. If the load impedance is smaller than
twice the tube's impedance, there is more dis-
tortion; if it is equal to the tube's impedance,
the amount of distortion due to second harmonic
currents will be about 15 per cent., this latter
figure being calculated from some curves on the
tube to be published in the Proceedings oj the I.
R. E. ("Development of a New Power Am-
plifier Tube," Hanna, Sutherlin, and Upp). The
impedance of many loud speakers, at the very
low frequencies, will be about the same as that
of the 250 type tube (2000 ohms) and therefore
there will be about 15 per cent, second harmonic
current generated by the tube. However, the
sounds created by musical instruments contain
many harmonics and the ear itself probably
generates others, so it may be that the above
figure of distortion is not large enough to be
serious.
The 210 push-pull arrangement has an ad-
vantage over the single 250 when the filaments
are to be operated on raw a. c. In the push-pull
amplifier, any hum due to the a. c. operation of
the filaments is cancelled out, while with the
single tube arrangement this does not occur.
However, the 250 tube uses a heavy ribbon type
filament (similar to that used in the 280 type
tube) which has a high thermal inertia tending
to prevent the production of any a. c. hum when
its filament is operated on raw a. c. The 250 type
has a low plate impedance, (about 1800 ohms)
and can therefore be used with ordinary loud
speakers without any need of an impedance-
adjusting transformer. Two 2io's in push-pull
have a plate impedance of about 10,000 ohms
and in this case it is best to use an impedance-
JUNE, 1928
THE NEWEST POWER TUBE
75
adjusting output transformer to adapt the tube
impedance to that of the loud speaker. Although
an impedance adjustment is not necessary when
using a 250 type tube, it is necessary to use an
output device to protect the windings of the
loud speaker from the high plate current of the
250 tube.
COMPARISON OF SENSITIVITY
UNDER this caption we discuss how the two
arrangements compare with regard to
power output for a given input voltage. Let us,
therefore, calculate the power output, fora given
input, for both arrangements. If each arrange-
ment works into a load impedance equal to
twice fhe tube impedance, then, per volt input
squared, there will appear in the load the
amounts of power, as indicated below.
ARRANGEMENT POWER IN LOAD. PER
VOLT SQUARED, ON GRID
OF TUBE
0.8 milliwatts
3.0 milliwatts
Single 250
Push-pull 210's
In this table the 250 shows up very poorly,
being only about one-quarter as sensitive as
2io's in push-pull. However, the turns ratio
of the average push-pull input transformer
available to-day is lower than an ordinary trans-
former and if we assume that with a single tube
the input transformer has a ratio of 4 and that
the push-pull transformer has a ratio of 2
(many push-pull transformers have a lower ratio
than this) between the primary and one side of
the secondary, we then obtain the following
figures:
ARRANGEMENT
Single 250
Push-pull 210's
POWER IN LOAD, PER
VOLT SQUARED, ACROSS
TRANSFORMER PRIMARY
12.8 milliwatts
12.0 milliwatts
These figures give a truer picture than those
given previously. The difference between the two
arrangements — a matter of 0.8 milliwatts per
volt squared — is too small to be appreciable to
the ear but at least we may be sure that an ampli-
fier using a push-pull arrangement wilth average
transformer ratios and with 2 10 tubes won't give
any greater volume, with a given input, than an
amplifier using a single 250 tube.
This analysis, summarized in the accompany-
ing table, shows the 250 tube to be about equal
to a 210 push-pull amplifier in most respects
excepting that of cost.
The complete characteristics of the 250 tube
are given in the table accompanying this article
which shows that this tube requires a plate volt-
age of about 450 volts and takes a plate current
of 55 mA. The power supply must provide this
amount of current and voltage. The loud speaker
must be isolated from this high plate current
by an output device.
In some cases it will be found possible to sub-
stitute a 250 type tube for a 210 tube in an
amplifier, but frequently this will not be possible
because the 250 takes three times as much plate
current as a 210 and the rectifier-filter system
may not be able to supply sufficient voltage at
this higher current drain. The higher current
drain may reduce the voltage output of the
power unit from 450 volts, when 3210 type tube
is used, to 300 volts or so and it is not worth
while to operate a 250 at this voltage. Under
such conditions the tube cannot deliver much
more power output than a 210 type tube,
operated at 450 volts.
ALLOW ONE WATT PER LOUD SPEAKER
"THE 250 type can be used in a properly
1 designed push-pull amplifier and such a use
for the tube should prove useful where sufficient
power is required for the operation of several
loud speakers or for auditorium work. A push-
i CHAR ACT
ERISTICS
OF THE TYPE
RECOMMENDED
Plate Voltage
Negative Grid Bias
Plate Current
Plate Resistance (a-c)
Mutual Conductance
Voltage Amplification Factor
Max. Undistorted Output
filament
Max. Overall
Base
MAXIMUM
250 300
45 54
28 35
2100 2000
1800 1900
3.8 3.8
900 1500
7.5 Volts
Height 6}"
Large Standard UX
350
63
45
1900
2000
3.8
2350
100
70
55
1800
2100
3.8
3250
1 .25 Amperes
Diameter 2}J'
450
84
55
1800
2100
3.8
4650
Volts
Volts
Milliamp.
Ohms
Micromhos
Milliwatts
Filter Choke Coils
15 henries or more
To
Receiver
GENERAL CIRCUIT REQUIREMENTS FOR THE 250 TYPE TUBE
All values are indicated except the voltage dividing resis-
tances which vary according to the receiver to be supplied
Comparing the 250 Type Tube With Other Power Tubes
IN THIS article the new type 250 power amplifier tube is compared with other power
tubes now available. A summary of the points developed more fully in the article
follows:
(a). The maximum power output of
a type 250 tube is 4.6 watts, which is
about three times as much as can be
obtained from a 210 type tube and
about seven times as much as can be
obtained from a 171 type tube.
(b). The power output of a single
250 is about equal to the power that
can be obtained from a push-pull
amplifier'using 210 tubes.
(c). The power supply equipment
necessary for the operation of the 250
type tube is about the same as is re-
quired for the operation of a push-pull
amplifier with 210 type tubes.
(</). Because ordinary transformers
are generally cheaper than push-pull
transformers, it is cheaper to construct
a power amplifier with a single 250
type tube than it is to construct a
push-pull amplifier with 2io's.
(e). An amplifier using a 250 will
give excellent quality. When the tube
is worked into a load impedance equal
to twice the tube's plate impedance,
rated output will be delivered to the
load without creating more than 5
per cent, of second harmonic current.
(/). The volume output of a single-
stage amplifier using a 250 will be
about equal to that from a push-pull
amplifier with type 210 tubes, assum-
ing that the input voltage is the same
in each case and that the transformer
feeding the 2 50 has a ratio of 4 and the
input push-pull transformer has a ratio
of 2 (average figures).
(/>)• A single 250 tube will supply all
the power, with plenty in reserve,
that will be required for the operation
of any radio receiver in the home.
Where only moderate volume is re-
quired, smaller tubes such as a 171,
may be used but where reserve power
is desired to take care of greater
volume, the type 250 may be used.
76
RADIO BROADCAST
JUNE, 1928
pull Amplifier with 250 type tubes will be
able to deliver to a load about 12 watts of
voice frequency power — which is no mean
figure! A push-pull amplifier using 210 type
tubes, outputting about four watts, can
be used to supply about four loud speakers,
and a push-pull amplifier with 250 tubes
will be able to supply about fifteen loud
speakers, assuming in both cases that each
speaker will require about one watt of energy.
In a home installation a single 250 tube
should give all the power that will ever be
required, with plenty in reserve.
Several manufacturers have already an-
nounced apparatus suitable for use with the
250 type tube. The General Radio Com-
pany has designed a complete line of
transformers, filter units, and output de-
vices for use with the 250 tube and a
description of this apparatus will be found
in the New Apparatus section of this issue.
The Silver-Marshall Company has de-
signed two amplifiers for the use of the 250
tube; one a single-stage affair, and the other
a complete two-stage amplifier. The two-
stage amplifier is illustrated herewith. It
uses a type 226 tube in the first stage and
a 250 in the second stage. Plate supply is
LEFAX RADIO HANDBOOK — (Seventh Loose-
Leaf Edition). Published by Lefax, Inc.
Philadelphia, Pennsylvania. Subscription,
$5.00 a year.
IS Lefax Handbook is in the familiar
form of a loose-leaf notebook about seven
by five inches. The first chapter, "What
Radio Does," is largely a summary of the various
uses of radio communication, from the distribu-
tion of time signals to television, with some dis-
cussion of special devices like chain broadcasting.
Next, under " Fundamental Principles of Radio"
the behavior of direct and alternating currents,
waves, and modulation methods is described.
The following chapters are on " Elements of
Receiving and Transmitting Apparatus," "As-
sembly of Receiving Sets," "Operation of Re-
ceiving Sets and Their Accessories," "Antennas."
The next-to-the-last section contains conversion
tables, definitions of radio terms, codes, formulas,
tube characteristics, etc. A complete index is
supplied. The material is gleaned from such
journals as the Proceedings of the Institute of
Radio Engineers, the Bell System Technical
Journal, Bureau of Standards publications,
RADIO BROADCAST, manufacturers' bulletins, etc.
It is clearly abstracted and an extensive survey
of practical radio engineering material is crowded
into this loose-leaf book. The editor is Dr. J. H.
Dellinger, Chief of the Radio Laboratory of the
Bureau of Standards. The system is based on the
issuance of sixteen sheets a month, ready to be
inserted in the binder. Obviously the rate of
progress of radio technology is such as to require
some such scheme as a supplement to scientific
textbooks which can appear only in widely
separated editions.
RADIO ENGINEERING PRINCIPLES, by Henri
Lauer and Harry L. Brown. Second Edition,
January, 1928. McGraw-Hill Book Co.,
Inc. 301 pages. $3.50.
THIS text, first issued in 1919, follows
Morecroft into a second edition. Unfor-
tunately the death of one of the authors,
Harry L. Brown, occurred just before the volume
appeared. With Mr. Lauer, he was able to com-
IKPUT 1.5U.AC. 2.25U.AC.
1 t > I i
+135 +90+45 B- SPEAKER
'
Boole Reviews
plete a creditable piece of work before he died.
The book is less extensive than Morecroft's, but
it is excellent for those whose requirements are
satisfied with a shorter and less expensive text.
The treatment is based on the electron concep-
tion of matter, with only moderate resort to
mathematics and no recourse to mechanical
analogies, with which, frequently, the student is
even less familiar than with the radio theory he
wants to learn. The book, as the title indicates,
is concerned with principles rather than with
concrete apparatus. It begins with a considera-
tion of the underlying electrical theory, the
properties of oscillatory circuits, antenna sys-
tems and radiation, proceeds to a description
of damped and continuous wave telegraphy,
devotes four long chapters to vacuum-tube
theory, and ends with chapters on radio tele-
phony and miscellaneous applications of radio
The principal additions to the first edition
are in the chapters on three-electrode tubes.
Numerous special topics, such as aircraft radio
compass work, the mathematical theory of the
push-pull amplifier and frequency doubler, the
theory of the balanced modulator, piezo-electric
resonators and oscillators, are adequately treated.
The book is a very scholarly' presentation. Pages
69-73 contain one of the few adequate descrip-
tions of the wave antenna to be found in radio
texts. The references to little known articles,
especially foreign sources, are alone sufficient
to warrant inclusion of the second edition in
every radio engineer's library.
A POPULAR GUIDE To RADIO, by B. Francis
Dashiell, The Williams and Wilkins Company,
Baltimore, 289 pages, $3.50.
THIS book is written for the non-technical
reader, according to the publishers. The
author is only incidentally a radio man; his reg-
ular employment is in the Weather Bureau at
Washington. The job of presenting the principles
and mechanism of radio appears to this reviewer,
who is a professional radio man and technically
inclined, to have been competently done. Ap-
parently Mr. Dashiell knows quite as much
about the art as if he had lived in it all his life.
But it is not clear, and this book does not make
obtained from a rectifier-filter system using
two type 281 tubes in a full-wave circuit.
A glow tube is used. The single-stage am-
plifier is similar to the two-stage unit that
is illustrated except that the apparatus for
the first stage is omitted. This latter am-
plifier may well be used to replace an
unsatisfactory last-stage amplifier in any
radio receiver. From both of these ampli-
fiers can be obtained the necessary B volt-
ages for the operation of the other tubes in
the receiver proper, and in addition the
two-stage amplifier will also supply a. c.
voltages for the filaments of any a. c. tubes
that may be used in the set. The two-stage
amplifier is also especially satisfactory for use
with a phonograph pick-up to play phono-
graph records. Both of these amplifiers can be
home constructed with little trouble, from
data obtainable from Silver-Marshall through
RADIO BROADCAST.
A COMPLETE A.C. AMPLIFIER
This commercially available unit
employs one cx-35o as the power
tube. The second and third sets of
binding posts at the top, reading
from the left supply a.c. filament
voltages for the set. This unit is
from Silver-Marshall
it clearer, just how a technical subject can be
expounded to a non-technical audience. In so
far as A Popular Guide to Radio elucidates and
instructs, it is moderately but quite definitely
technical. It is not made less technical by the
insertion of a frontpiece showing Carlin and
McNamee broadcasting a football game. If
"non-technical" means free from mathematics,
then the book is non-technical, true enough.
But this merely results in passages like the fol-
lowing description of "Impedance in an Alter-
nating Current Circuit": "A circuit may have
inductance and capacity in addition to its
natural electrical resistance when an alternat-
ing current is flowing. When this combined re-
actance and natural resistance operates to ob-
struct the flow of an alternating current it is
known as the impedance. However, as inductive
and capacitive reactances are the reverse of each
other, the total reactance of a circuit is the dif-
ference between the two reactances measured in
ohms and giving the impedance designation to
the predominating reactance. The electrical re-
sistance in ohms cannot be added to this total
reactance to obtain the impedance. Graphically,
they should be combined as straight lines in pro-
portionate lengths. Assuming them as two
forces acting together at right angles, their
resultant is the impedance." This sort of writing
is neither wholly accurate, readily comprehen-
sible, nor compact. Its somewhat puffy and la-
bored quality arises from the fact that it is the
wrong way of doing the thing. And incidentally
impedance is just as natural as resistance.
When Mr. Dashiell does not attempt the im-
possible he turns out a creditable piece of work.
There is a lot of sound, up-to-date informa-
tion, with a few platitudes intermingled, and
here and there a debatable statement, such as
that on page 170 about the neutrodyne circuit.
where the names of Hogan. Hazeltine, and At-
water Kent are mentioned, and not a word about
Rice and Alexanderson. The photographs are
well-chosen and the figures nicely drawn. After
reading it one is left with the impression that
this is a worthy book, but exactly for whom was
it written?
— CARL DREHER.
RADIO BROADCAST Photograph
By W. H. WENSTROM
Lieut., Signal Carpi, U. S. A.
IOME of the most fascinating fields of radio
lie outside that narrow band in which the
broadcasting stations do battle. Voice and
music from Europe, code from tossing ships or
lonely airplanes, faint signals from amateurs at
the antipodes or explorers in arctic cold and
equatorial heat — all these are echoing along the
lanes of the ether. To hear them we must have a
receiver that is simple, reliable, accessible, effi-
cient and flexible. As the Navy recently applied
the name "Cornet" to an unusually flexible
transmitter, so this receiver, able to shift rapidly
from one frequency to another — to play a vari-
ety of tunes — is also called "Cornet."
The general design is apparent from the circuit
diagram, Fig. I, and the photographs. For sim-
plicity we go back to that venerable amateur
mainstay, a capacitatively controlled regenera-
tive detector with one stage of audio; and we
avoid tuned radio-frequency and screen-grid tube
arrangements. On the front panel are one main
and two auxilliary controls, while two adjusting
controls are on the sub-panel.
Reliability is secured by using the best parts
that we can buy. We avoid the pitfalls of some
poorly made pig-tail condensers, noisy grid leaks
and the like. Each radio part must meet two
exacting standards — the electrical and the
mechanical.
Accessibility is often neglected in radio design.
The best set in the world will occasionally develop
trouble, which must be located and remedied at
once. This set is accessible because of sub-panel
construction and general openness of design.
In pure efficiency, the regenerative detector
has never yet been equalled. Unusual features of
this set include a micro-vernier condenser of
about 3.o-mmfd. maximum capacity and a grid
biasing potentiometer which controls the sensi-
tiveness, selectivity and oscillating characteris-
tics of the detector tube. All three tuning con-
densers are mounted directly against a panel
backed with aluminum which in turn is connected
through the sub-panel brackets to ground; so
that body capacity, as found in the usual short-
wave receiver, simply does not exist.
Above all, the receiver is flexible. The Silver-
Marshall plug-in coil system is used on account
of its electrical efficiency, convenience, and com-
pactness. The set is primarily designed to cover,
with four coils, the range from 14 to 200 meters.
This range is obtained by using a tuning con-
denser somewhat larger than usually recom-
mended by Silver-Marshal. Additional bands
can be covered, as desired, by extra coils.
CONSTRUCTIONAL DETAILS
HpHE arrangement of parts is shown in the
1 photographs. First, drill the metal and insu-
lating front panels; then assemble the front
panels, the sub-panel brackets, and the sub-
panel. All are bolted together with small nick-
eled machine screws. For best appearance, the
front panel should slope back about 15 degrees
from the vertical.
Three Cardwell condensers, with their asso-
ciated General Radio dials, are mounted on the
front panels. The right condenser, viewed from
front panel, is of o.ooo25-mfd. maximum capac-
ity, and may be either the old, flat-plate type,
which sells very cheaply in many stores, or the
new taper-plate type. The left condenser should
have a maximum capacity of about 0.000165
mfd. This is obtained from an old type 0.00025
by removing two rotor and two stator plates,
leaving four rotors and three stators. If the old
type 0.00025 cannot be secured, the new taper-
plate 0.00015 may t>e used, though with this
latter condenser, minute uncovered frequency
bands will appear between the coil ranges. Of
course, the coils may be slightly redesigned to
cover these breaks; or the standard S-M coils
(. r HE set described here by Lieut. Wenslrom has
•*• two features unusual in receivers designed to
cover the high frequencies: (a), a potentiometer
across the A battery to adjust the bias voltage on
the gird of the detector so that the best operating
point may he found; and (b), a small vernier con-
denser across the main tuning condenser to enable
the operator to tune very closely to a given fre-
quency, or to follow a fading signal with greater
ease. On lest in the Laboratory, this receiver worked
very well, 5 sw at Chelmsford, England, being heard
at 6 p. m. E. S. T., without difficulty. The biasing
potentiometer adds much to the sensitivity of this
set. It is common amateur practice to use a high-
ratio transformer, working out of the detector into
the first audio tube. Lieut. Wenstrom has used a
low ratio transformer which provides better repro-
duction when the set is used for receiving short-
wave broadcast transmissions. A vernier dial with
a greater reduction ratio than the one employed —
such as the Karas — might make tuning somewhat
easier, perhaps even obviating the necessity for the
auxiliary tuning condenser.
— THE EDITOR.
77
may be used, with some loss of tuning range.
The center condenser is a Cardwell "Balancet"
of the smallest size, with all plates removed ex-
cept the back stator and the front rotor. The
"phones" jack is placed at the lower right corner
of the front panel, insulated from the metal
by a bushing of bakelite, hard rubber or fibre.
Because the set must often be switched on and
off without jarring it or disturbing the wave-
length setting, an external knife switch is used
by the writer rather than a filament switch on
the panel.
On the upper side of the sub-panel are mounted
the coil socket, the two tube sockets, two fila-
ment ballasts, two grid leaks and knobs for the
antenna condenser and the potentiometer. On
its lower side are the potentiometer, the audio
transformer, the r.f. choke, the grid condenser,
and the antenna coupling condenser, for which
a Silver-Marshall midget is chosen because of its
low minimum capacity. The binding posts are set
into the back edge of the sub-panel. The ampli-
fier grid leak is clipped in when wanted for phone
work; the glass casing of the detector grid leak
should be washed free of paper and glue.
Wiring is best done in definite steps. The fila-
ment circuit is first wired and tested. Then come
the other circuits in natural order: antenna-
ground, detector grid, detector plate, amplifier
grid, and amplifier plate. Grid leads, of course,
are reasonably short, and all leads are fairly
straight without sharp angles. Though No. 14
wire is used in places for rigidity, most of the
wiring is done with solid, rubber covered wire
of about No. 20 size, known in telephone par-
lance as "pothead" wire. It is plainly absurd to
insist on large wire leads in series with coils, high
resistances and the like. Acme Celatsite is also
quite satisfactory and convenient.
The four plug-in coils are those supplied in the
Silver-Marshall No. 1 17 short-wave set, rewound
with No. 26 enameled copper wire except as
otherwise indicated. They are completely de-
scribed in the coil table. Three optional extra
coils are also listed.
The detector tube is preferably a Ceco type
" H ," though it may be any good make of high-mu
tube, or even one of the 2OI-A type. [The 2OI-A
is satisfactory as a detector in this circuit, of
course. If the Ceco type H, or other special
detector tubes, or even a standard high-mu tube
is used, the "gain" will increase. However, in the
latter case, quality may be impaired to some
extent when this set is used for headphone recep-
tion.— Editor.] The amplifier tube is a 2OI-A.
78
RADIO BROADCAST
JUNE, 1928
COIL TABLE
COILS for
the first four
bands listed below are those
upplied in the Silver-Marshall No. 117 short-wave
coil set,
rewound with
No. 26 enameled copper wire
, except as otherwise
indicated in the last column.
BAND
COIL RANGE
GRID TURNS
TICKLER TURNS
REMARKS
20m.
14-28 m.
3
3
No. 24 wire, with triple (the
standard S-M) spacing
40m.
26-52 m.
6
5
Grid 1 less; tickler 2 less than
S-M standard
80 m.
51-110 m.
15
8
Grid 3 more; tickler 2 less.
160m.
100-200 m.
36
16
Grid, 10 more; tickler same.
Shortest wave
1O-21 m.
2
3
No. 24 wire; quadruple spac-
ing.
Ship waves
550-1100 m.
Standard S-M No. 111-D
Long wave
1100-2000 m.
approx. Standard S-M No. 111-E
No cabinet is included in the plans, as a small
writing desk serves the purpose, and the builder
may have his own especial preferences anyhow.
OPERATION
TO place the set in operation, connect the
6-volt filament leads, see that the tubes light,
and then connect the 4j-volt B battery. Next,
CALIBRATION CURVE
40 METER COIL
50
35
25
0 10 20 30 40 50 60 70 80 90 10Q
DIAL SETTING
FIG. 2
Calibration curve of the 4o-meter coil and con-
denser combination used in this set. Slight electri-
cal differences in parts used by constructors may
make their calibration different from this
place one of the coils, say the 4O-meter one, in
the coil socket. With the left-hand condenser set
at any reading, increasing the right-hand con-
denser should put the set into oscillation with a
weakly audible "plop." The potentiometer is
adjusted to minimize this "plop" so that the set
goes smoothly into and out of oscillation. In
general, the potentiometer arm is turned toward
the positive side of the circuit for phone work and
slightly toward the negative side for code re-
ception. As the left dial is moved to a higher
reading, a correspondingly higher reading on
the right dial will usually be necessary to produce
oscillation. If the r.f. choke is doing its work,
there should be no "dead spots" in the tuning
range. At any wavelength setting of the left
dial, the most sensitive right dial setting for
phone is just below or at the oscillating point;
for code, just above it.
With these preliminary tests completed, the
set is connected to the ground and to the antenna,
a single wire anywhere from 20 up to 750 feet in
length. [A small indoor antenna with this set in
most locations will probably serve very well
for all purposes.. — Editor.] The 4O-meter coil
being in place, signals should be heard as the
left dial is moved over its entire range, for this
band is busy at any hour of the day or night.
If any "dead spots" now occur, blame them on
the antenna, and decrease the antenna coupling
condenser to the point where they are not trou-
blesome. This antenna condenser is always set
at the maximum capacity which will not interfere
with the convenient operation of the oscillation
control. After a signal has been tuned-in wilh
the left dial and brought to full strength with
the right one, apply the finishing refinement of
tuning with the center dial and its diminutive
condenser. This control is so fine that a single
beat note spreads over 5 to 10 degrees, and the
"zero beat" for phone reception is easily pro-
duced.
CALIBRATION
FOR maximum usefulness all coils should be
carefully calibrated. The data, including the
settings of the left dial for various wavelengths,
may be plotted as a graph, which is scientific
and thorough (see Fig. 2); or they may be listed
in a table, which is more convenient to read.
Such a table for the 4O-meter coil employed by
the writer is: o-26m., i^-^om., ^6-^-j.^m., 45-
4Om., 5Q-43m., ioo-$2m. While this table is
approximately correct for the set here pictured,
changes in detector tube, wiring and variations
in coils used by those who duplicate this set, or
other circuit constants would make it practically
useless for another. Each set must be calibrated
individually.
First, a wavemeter must be bought, borrowed
or made. Then, the left receiver dial is set at
some convenient reading (say O), the antenna
condenser is set to minimum, the vernier to 50,
and the right dial to two points above oscillation.
Place the wavemeter coil in what would be a
FIG. I
Circuit diagram of Lieut. Wenstrom's receiver
FIG. 3
General instructions on altering the coil form
for the 20-, 40-, 80-, 160- and lo-meter bands.
(See the coil table on this page)
prolongation of the set coil, and rotate the wave-
meter dial slowly. Two "plops" are heard, one
as the set goes out of oscillation and another
as it goes back into it. Now move the wave-
meter a little farther away, and repeat the per-
formance until the two "plops" are practically
one. Or note the point midway between the two
" plops." This point on the wavemeter scale is the
wavelength to which the receiver is tuned. The
left dial is now moved to a new setting and every-
thing is repeated. All the coils are calibrated in
the same way. If you wish to find the receiver
dial reading for any particular wavelength, set it
on the wavemeter and rotate the receiver dial.
A wavemeter is simple enough to make. The
basic circuit consists essentially in a coil and a
variable condenser. The homemade product must
be calibrated from a standard one. By checking
both against the receiver, data is secured for
a homemade wavemeter curve similar to the
curve of Fig. 2. Of course it is possible to cali-
brate one's receiver by picking up signals from
well-known stations. For example the amateur
4O-meter band is bounded by NAA at about 37.4
meters at one end and by wiz at 43 meters at
the other. Standard frequency signals are sent
out at regular intervals by wwv, the Bureau of
Standards station, (see page 84) and others.
WHERE TO FIND THE STATIONS
WE NEED have no illusions about the qual-
ity of short-wave broadcasting, nor any
fear that it will replace the present system of
allocation of stations in the 1500-550-^. band.
Fading is usually quite severe, and the signal
strength of distant stations varies widely from
day to day. In America, WGY on 21.9 and 32.77
meters and KDKA on 25 and 62 meters transmit
JUNE, 1928
THE "CORNET" MULTIWAVE RECEIVER
79
THE CORNET MULTIWAVE
RADIO BROADCAST Photograph
RECEIVER
the regular programs of their standard-wave
broadcast plants. Their signals have world-wide
range, and quality dependent on the atmospheric
and Heaviside layer conditions. In England,
5 sw at Chelmsford carries the regular London
programs on 24 meters, and is heard any weekday
afternoon up to 7:00 p. m. E. S. T. Reception of
this station is really good perhaps one or two
days a week. The signal of PCJJ at Eindhoven,
Holland, is weaker and more variable than that
of 5 sw. It comes through at present late Tues-
day, Thursday, and Saturday afternoons (East-
ern time). So far, these two have been the only
foreigners regularly heard, and their programs
have appealed chiefly by their novelty. Perhaps
within a few years most important nations will
have high power, short-wave telephone trans-
mitters, and fading will be minimized by sepa-
rated, synchronized transmitters or some such
scheme. Then international broadcasting will
truly begin, and this receiver will be able to
choose its programs between five continents.
For one who reads code the pleasures of this
receiver, and of all radio, are greatly extended.
NAA at Washington, on approximately 24.9, 37.4
and 74.8 meters, broadcasts weather at 8. 15 and
10:30 a. m. and p. m.; time at 12:00 noon and
10:00 p. m.; and press at 1.30 a. m., E. S. T.
Station NPG at San Francisco, on 36 and 72
meters, sends weather at 6:15 and 7:30 a. m.
and p. m., P. S. T. To keep up to date on these
schedules, one must consult the weekly radio
sections of large newspapers. [A list of Navy
transmissions appeared in this magazine for
May, 1928. — Editor.] The biggest nuisance in
the short-wave spectrum is the harmonics of
long wave broadcasting stations, which delude
the listener in this short-wave section of the band
into thinking he hears something new.
Many important exploring expeditions trans-
mit code. Most of them favor the waves around
30 meters. This summer there will be at least
one expedition near the North Pole, one near the
South Pole, plenty of transocean flights, and
at least one round-the-world dirigible flight.
Some far distant amateurs come in from
18 to 24 meters during many of the daylight
hours, though most of these experimenters use
the 4O-meter band. In this region, Europeans
between 43 and 47 meters, just above the United
States band, begin to be heard about an hour or
two before sunset. Before sunrise signals from
the Australians and New Zealanders come
through around 33 meters. There are some
United States amateur telephone stations be-
tween 84 and 85 meters.
Six hundred meters is the international marine
calling wave. Rapid dots and dashes from ship
sparks are always audible near the seacoast. On
this wave, too, sounds at times the staccato
sos for which broadcasting stations shut down.
Copying signals from a ship in distress and the
vessels going to her assistance is the most exciting
thing in radio. Of course it is in no sense a pleas-
ure; the lesson of Robert Louis Stevenson's
Merry Men is plain. For actual message handl-
ing, ships use waves around 700 and 900 meters.
On looo meters in foggy weather, the coastal
radio beacons flash their distinctive groups.
Radio compass bearings are given on 800 meters.
For data on the coils which cover all the bands
discussed in this article, see the table on page 78.
This "Cornet" multiwave set opens the door
to reception interesting and unlimited, or limited
only by the skill and patience of the operator.
And what more could he ask?
THE PARTS WHICH WERE USED
THE following list of parts gives the apparatus
used in the writer's receiver. Naturally, other
parts, electrically and mechanically similar may
be used. Coils and condensers mentioned here
are of well-known manufacture and have been
altered in ways indicated in the text.
Ci Cardwell type 141-6 25O-mmfd. variable
condenser, (revised as indicated in the text)
Cj Cardwell Balance! j-mmfd. (approx.) vari-
able condenser
C3 Sangamo i5O-mmfd. fixed condenser
Ci Cardwell type 141-6 25O-mmfd. variable
condenser
Ci Silver-Marshall type 340 midget condenser
LI, LI Coils wound on Silver-Marshall forms
(as described in text)
Ls Silver-Marshall Type 275 R.F. choke
Ri Tobe Tipon 6-megohm grid leak
R-i General Radio type 301, zoo-ohm potenti-
ometer
R3 Daven J-ampere filament ballasts with
mountings
Ri Tobe Tipon 0.5 megohm resistance (op-
tional, see text)
Ti Thordarson small type 2:1 audio trans-
former
I Silver-Marshall coil socket type 515
I Benjamin navy spring type socket
1 Hoosick Falls navy plain type socket
2 Grid leak mountings
2 Knobs, Kurz-Kasch, ij-inch
i • General Radio type 303 4-inch vernier dial
I General Radio type 317 4-inch plain dial
I General Radio type 310 Zj-inch plain dial
5 Eby plain binding posts
i Pacent open circuit jack
i Insulating bushing for jack
i panel 7" x 14", hard rubber or bakelite
i back panel, 7" x 14", aluminum
1 Sub-panel, 4" x 14", hard rubber or bakelite
2 Benjamin adjustable sub-panel brackets
RADIO BROADCAST Photograph
HOW THE MULTIWAVE SET LOOKS FROM THE TOP
Four of the coils used are shown with their convenient adhesive tape labels
AN
OF WIDE USE TO
EVERT RADIO EX-
PERIMENTER
With an inexpensive milliam-
meter arranged as described in
this article, a portable and
very useful measuring set can
be made. The set will measure
practically all of the common
d.c. voltages and currents up
to 5 amperes and 1000 volts.
It is especially useful in test-
ing B power units. The crystal
detector circuit malfes this unit
useful as an r.f. resonance in-
dicator in transmitter circuits
From Milliammeter to Multimeter
lERHAPS one of the fundamental reasons
why electrical science has grown so tre-
mendously in its comparatively short life
span is the ease and accuracy with which elec-
trical measurements can be made. An ability
to determine accurately the magnitudes and re-
lations of the quantities involved in any work
naturally leads to intelligent interpretation and
utilization of those quantities. Applying the last
statement to the radio worker, an ability to meas-
ure the B-battery voltage at 17 volts per 22-volt
block is much more conducive to results than
wondering if low B batteries are spoiling the re-
ception; and plugging-in to measure the plate
current of a tube can be made to save many
minutes, if that particular tube has gone dead.
It is surprisingly simple to take a low-range
milliammeter and make an almost universal
measuring instrument of it. The instrument can
be made to measure the whole gamut of d.c. radio
voltages, from the voltage of a dry cell on up
through the various A, B, and C voltages to
those used for plate supply in transmission work.
Starting with a meter of one milliampere full-
scale deflection, the current range can be run up
as high as desired ; and then the meter can be used
for indicating a few other quantities on the side.
The extension of the milliammeter range to read
both voltages and currents of various magnitudes
is accomplished by means of what are known as
multipliers and shunts.
Suppose two resistors are put in parallel in a
circuit; the current will naturally divide, part
going through one resistor and the rest through
the other. An idea as to how the current divides
G. F. Lampkin
through the two paths can be had if the values
of the two resistors, RI and R2, are known. The
current, Iz, in resistor R2 is equal to:
Ri
RJ
X TOTAL CURRENT
And similarly, the portion li in the path RI is
equal to:
Ri
x TOTAL CLRRENT
The idea of the shunt is to bypass a part of the
total current around the milliammeter, and let
only enough current go through the latter to give
full-scale deflection when the total current to be
measured is flowing. If the total current is less
than that required to give full-scale deflection,
with a given shunt, the meter reading will be less
in the same proportion. By properly choosing the
resistance of the shunt, the meter can be used to
read any magnitude of total current. If the shunt
resistance is very low, the meter can be used to
read large total currents; or, conversely, if the
shunt resistance is high, small currents can be
measured. With no shunt, the meter of course
indicates the current as shown by its scale.
Another consideration in choosing the shunt,
besides its resistance, is its physical size. The
shunt must be of large enough carrying capacity
that it does not get hot when passing its part of
the current. If it should get hot, its resistance
would change and destroy the accuracy of the
readings.
To use the milliammeter as a voltmeter re-
quires a multiplier. The latter is simply a re-
sistance that is connected in series with the
80
meter. Suppose the milliammeter, with a current
scale of o-i milliamperes, has a resistance of 3
ohms. With full-scale deflection, the voltage drop
across the meter is o.ooi amperes times 3 ohms,
or 0.003 volts. Another way of stating the re-
quirement for full-scale deflection of this meter
is, therefore, to say that 0.003 volts must be im-
pressed across it. When the multiplier is placed in
series with the meter, its resistance causes a
voltage drop, and leaves remaining a small value
of voltage to operate the meter. By choosing the
right values of series resistances, the meter can
be used to measure a wide range of total voltages.
For a meter resistance of RI ohms and a multi-
plier resistance of R2 ohms, the voltage on the
milliammeter will be:
R,
Ri + R:
x TOTAL VOLTAGE.
The economy resulting from the use of shunts
and multipliers is obvious. A o-i Jewell d.c. mil-
liammeter can be had for $7.50 list. With this one
meter as an indicator, as many shunts and mul-
tipliers as desired can be made, at a fraction of
the meter cost, and each shunt, or multiplier, will
extend the use of the meter.
The meter shown in the photographs is de-
signed to cover pretty well the field of d.c. meas-
urements in radio. In addition, it utilizes a fixed
crystal detector to yield an instrument some-
what similar to a thermo-galvanometer. While
it cannot, in the latter role, be calibrated to read
actual current values, still it is extremely useful
in radio- and audio-frequency measurements,
for showing relative values, or for indicating re-
JUNE, 1928
FROM MILLIAMMETER TO MULTIMETER
81
sonance or null settings. The plug-in system
which is used makes it a matter of seconds to
change from one range to another, or from volt-
meter to ammeter, or a.c. indicator. In the par-
ticular instrument shown, the layout provides
for five current ranges: o-i mA., o-io mA., o-ioo
mA., o-i Amp., and 0-5 Amps. The voltage
ranges are o-io, o-ioo, and o-iooo volts. The a.c.
indicator requires approximately 5 mA. a.c. for
full-scale reading. Fig. i gives the panel and
cabinet layouts.
In Fig. 2 is given the diagram of connections.
The double plug is simple to construct. The
material for it is cut to shape as shown in Fig. i .
and then two General Radio type 274? contact
plugs are screwed into the two threaded 3% slots.
The receptacles for the double plug consist of
General Radio type 274] jacks.
Only one connection to the double plug is
needed when the instrument is used as a volt-
meter or a.c. indicator, so the rear sockets for
these connections are left blank on the panel top.
Thus a total of fourteen 274] jacks will be neces-
sary. For appearance's sake, however, the blank
holes might be hidden by using four more jacks,
to which no connections are made. The negative
binding post is made common for all the functions
of the meter. It is brought out at both sides of the
panel to facilitate connections. The milliammeter
is placed in the negative side of the circuit so
that it will be at ground potential when the de-
vice is used as a voltmeter. The positive binding
posts are separated for the three functions of the
meter. This makes for safety in that it lessens the
chance of using the ammeter connection when
trying to measure a voltage. It also allows con-
necting the device in the circuit to measure both
voltage and current, and doing one or the other
by changing only the plug. The end of the car-
borundum detector marked "A" by the manu-
facturer goes to the positive binding post. The
o.ooo5-mfd. condenser is shunted across the
meter to protect it from radio-frequency currents;
its use is not an absolute necessity, however.
The supports for the shunts, multipliers, and
detector are made of bus wire. The com-
mon rear support for the three multi-
pliers is made of sheet copper or tin.
The multipliers used are Tobe Veritas
5-watt resistors. The power expended
in the resistor for the higest range is
looo volts times o.ooi amperes, or only
i watt, which is sufficiently low to
avoid heating the multiplier.
The table of Fig. 2 shows the shunts
that are used for the different ranges.
For the lower ranges, i.e., 10 and 100
milliamperes, No. 32 tinned hair wire
was obtained from the hardware store.
The lo-milliampere shunt is so long
that it must be wound on a form, the
dimensions of which are given in Fig. i.
The other shunts are short enough to be
suspended between their bus-wire sup-
ports. The smallest sizes of copper wire
consistent with freedom from heating
effects are used as shunts for the higher
ranges. Smaller sizes than these should
not be used; should larger sizes be
used, the lengths given in the table
must be increased. The lengths speci-
fied may be slightly on the long side,
in which case they should be clipped
when calibrating. All the connections
in the instrument should be soldered.
As shown in the photograph, the con-
nections between the top panel and the
meter are flexible; thus the top panel
can be turned over to an easily ac-
cessible position when adjusting the
shunts. It is wise to mark the sockets
J
THE FINISHED INSTRUMENT — INSIDE
plainly with the appropriate data — 100 Volts,
i Ampere, etc.
CALIBRATION
THE calibration of the meter is the most im-
portant part of the job. The straightforward
and accurate method is to compare the meter
directly with standard instruments. It should be
possible for the experimenter to obtain the use of
voltmeters and ammeters from a friend, a radio
dealer, radio laboratory, educational laboratory,
power company, or other such source. But, failing
in these, it is still possible to obtain reasonably
accurate calibrations. In any case, the readings
of the meter should not be relied upon for greater
accuracy than two or three per cent.
To compare the voltmeter ranges of the device
directly with a standard voltmeter, the two in-
struments should be put in parallel and con
nected to the voltage source, as in Fig. 3. The
source may consist of a storage battery or dry
cells, for the ten-volt range, and a bank of B bat-
teries, or a B device for the higher ranges. Both
meters should be connected when the readings
are made, and the latter should be taken nearly
simultaneously. It is not necessary to take more
than three or four points uniformly spaced along
the scale. If only one or two readings are possible,
these should be made near the top of the scale.
On a piece of graph paper a scale from o to 10
should be drawn on the horizontal axis, to corre-
spond to the meter scale. A scale from o to 1000
is drawn vertically to correspond to the readings
of the standard instrument. When the calibration
points for the lo-volt range are plotted, the verti-
cal scale is assumed to run from o to 10, that is,
the decimal point is placed by inspection, and
the curve is labeled o-io volt range. The points
for the loo- and looo-volt ranges are treated
similarly, so that the entire voltmeter calibration
is on one sheet. The calibration curves are really
straight lines running through the zero point.
One accurate point is sufficient to determine the
line, but more than one serves as a check. If all
the points do not lie on the line, the latter should
be made to run an average course through them.
The calibration curves for the particular meter
shown are given in Fig. 4. It must be borne in
mind that these curves will fit no other meter.
The drawing of the calibration curves is neces-
sitated by theinaccuraciesof the resistance values
of the multipliers. The i -megohm multiplier
should have yielded a full-scale range of 1000
volts, where in fact it gave only a range to 702
volts. In other words, its resistance is 702,000
ohms, and not 1,000,000 ohms. Incidentally,
when using a o-i milliammeter as indicator, the
number of thousands of ohms in the multiplier is
equal to the full-scale range of the voltmeter;
i.e., a looo-ohm resistor gives a i-volt range, a
io,ooo-ohm resistor a lo-volt range, etc. The dis-
advantage of the inaccurate resistor is only that
the calibration is not a multiple of 10. Once the
S-de.Vstock
2 Reou.rtd
CABINET
FIG. 1
Layout for panel and cabinet of the useful home tester described here. The pho-
tograph above shows the disposition of the shunts, meter, and fixed detector
82
RADIO BROADCAST
JUNE, 1928
A.C.
.
mfd.
--/VV^VWSAAA-<^
Volts
• 'VWWWWVH§>—
R3
VWNAA>V\\VU^)-
R2
I . ••.fVWWWW> — ©)—
Ri
6 volts
-Amps. or Mils.
SHUNTS
R, 10 mA. 7!* Feet No. 32 Tinned Hair Wire
R2 100mA. 4 Inches No. 32 " " "
R 3 1 Amp. 9 Inches No. 26 Copper Wire
R4 5 Amp. 7 Inches No. 20 ""
R5 10 Volts
Re 100 Volts
R 7 1000 Volts
MULTIPLIERS
Tobe Veritas
FIG. 2
Circuit connections and values of apparatus
instrument has been calibrated, readings may be
taken as accurately as with correct-value re-
sistors. If a standard voltmeter cannot be ob-
tained, new dry cells and B batteries may be
used as voltage standards. The voltage of a
single dry cell should be taken as 1.58 volts, and
that of a 22 j- volt B block as 23.7 volts. Voltages
of larger blocks should be taken in proportion —
47.4 volts for a 45-volt block, and so on. Some
half dozen calibration points should be taken,
and the average curve drawn. The method will
allow results of good accuracy. Of ten blocks
whose voltages were measured, the maximum
discrepancy from the voltage value given above
was only 0.7 of a volt. Taking the average of
several calibration points will tend to iron out
any discrepancies.
In the case of the shunts, their lengths can be
adjusted to make the scale come out even, so
that no calibration curves are necessary. Al-
though the milliammeter scale reads from o, 0.2,
0.4, up to I milliampere, it must be remembered
that with the shunt, say for 100 milliamperes,
the scale is read o, 20, 40, up to 100 milliamperes.
It is another case of placing the decimal point.
To calibrate the meter and shunts by direct
comparison the meter is placed in series with the
standard ammeter, as in Fig. 3. Suggested current
sources and loads for the current calibrations are
given. The load resistor is adjusted to give full-
scale reading on the meter. If the reading on the
standard ammeter is lower than the total current
should be, first open the load circuit, then melt
the solder and shorten the shunt. Or if the stand-
ard meter reads high, lengthen the shunt.
Reclose the circuit and check again. A few trials
will suffice to bring the reading to the dot. If
the load circuit is not opened before loosening
the shunt, the total current will pass through the
meter and ruin it. Each shunt must be adjusted
as above.
To calibrate the lo-milliampere shunt when
no standard meter is
available, place the
meter in the circuit,
plug in on the i-milli-
ampere range, and ad-
just the current to ex-
actly i milliampere.
Then plug-in on the
lo-milliampere range; if
the reading is high,
shorten the shunt — or
vice versa. Bring the
reading to exactly o. i
on the scale, correspond-
ing to i milliampere on
the lo-milliampere
range. Finally, re-check
the current on the lower
range. For the 100-
milliampere range, 'set
the filament voltage at
the socket terminals of
a 199 type tube at 3
volts. The previously
calibrated lo-volt volt-
meter may be utilized.
Then with rheostat set-
ting unchanged, remove
the voltmeter and place
the loo-range milliam-
meter in series with the
filament. Change the
shunt till the meter
reads 60 milliamperes.
Again re-check the volt-
age. The same procedure
may be followed in cali-
brating the i- and 5-
ampere scales, by using
larger tubes. The 2OI-A tube gives 0.25 am-
peres at 5 volts, or the 112 or 171 tubes 0.50
amperes at the same filament voltage. For the
higher loads, several tubes in parallel can be
used, and the currents added up. The accuracy
of this tube-load method is surprisingly high.
Of four Radiotron ux-2oi-A tubes picked at
random, the filament currents were 0.250, 0.250,
0.247, ar|d 0.249 amperes at 5 volts. For a ux-i 12
Amps. or Mils +Q
J Plug 9 J
10,000 Ohm
100,000 Ohm
1 Megohm
GENERAL RADIO PLUGS AND JACKS USED
Multimeter
Standard
VOLTMETER
CALIBRATION
it was 0.500 amperes, and for a ux-i7i it was
0.493 amperes, at the same voltage.
The a.c. indicator is .the part of the device
that needs no calibration. If it were calibrated,
the readings might be 50 per cent, off the next
day. It is, however, a most convenient attach-
ment. With a loop of wire connected to its ter-
minals and coupled loosely to a radio-frequency
circuit, it will show resonance points sharply.
This function is of course applicable to wave-
1100
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VOLT
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lOVol
Rang
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uj fiO(
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g 500
400
300
200
100
/5
S
S
//
/
s
X
'/
•'m
a Volt
tange
>
/
S
X
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x
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0 456789 II
SCALE READING
FIG. 4
Calibration curves made by the author for me-
ter used in the original model. These calibrations
are not standard, varying with apparatus used
by the individual constructor
meters. In tuning up a crystal-controlled trans-
mitter the indicator can be moved from circuit
to circuit down the line, as the tuning progresses,
and so may save several dollars and watts loss
that would be occasioned by the use of radio-
frequency ammeters in these circuits.
The complete meter shows up particularly well
in the measurement of B device voltages. It is a
high-resistance voltmeter — 1000 ohms per volt.
The current that it draws at the most does not
act to give untrue voltage readings.
An enumeration of the single quantities that
might be measured in radio work with the instru-
ment would require considerable space, as would
also detailing the connected experimental data
that are possible of determination by its use.
Multimeter
Load
Standard
Source
II
AMMETER
CALIBRATION
CURRENT CALIBRATION SOURCES AND LOADS:
10 mA.- DryCell,400-Ohm Potentiometer
100 mA.- 4.5-Volt Battery, 199-Tube Filament
1 Amp.- 6 - Volt Battery, 201- A, 171 Tube
5 Amp.- 6- Vclt Battery, 4-Ohm Rheostat
FIG. 3
How to calibrate the
home-made meter
set with a standard
Output
Transformer
Characteristics
AN OUTPUT trans-
former connecting a
loud speaker to a
power tube serves two
purposes: (a.), to keep the direct current
flowing in the plate circuit of that tube
from circulating through the windings
of the loud speaker; (6). to correct any
large impedance differences which may
exist between the speaker and the tube.
The user has a right to expect that the
use of the transformer will not perform
the tasks mentioned above at a loss in
either power or fidelity.
The curve shown in Fig. i shows the
frequency characteristic of the Pacent
1:1 output transformer. The upper curve
represents the voltage across 5000 ohms
when 15 volts were applied to the grid
circuit of a 210 tube which was properly
biased and taking about 20 miiliamperes
of plate current. The lower curve shows
the same characteristic translated in
TU. Anyone desiring to know the power
delivered to the output load resistance
may calculate it by dividing the voltage
squared by the resistance. The extreme
variation obtained in this manner is from
395 milliwatts at 60 cycles to 610 milli-
watts at 2000 cycles, or less than 2 TU,
which is quite good.
The loss in power occasioned by the
use of a transformer instead of placing
the loud speaker directly in the plate
circuit of the tube may be calculated by
dividing what one actually gets into the
5000 ohms by what would be obtained
without the transformer. The power output of a
tube working into its own impedance (in this
case the 5000 ohms is sufficiently near that of the
tube) is equal to
Strays'
rom
Wo
(V- eg)'
where
(i is the amplification factor of the tube
eg is the input volts r.m.s.
Rp is the tube impedance
Using this formula, the power into 5000 ohms
with 1 5 volts r.m.s. on the grid of the tube should
be 720 milliwatts. Actually we get only 395 at
60 cycles and 610 at 2000 cycles. These are losses
due the transformer of only 2.6 and 0.7 TU re-
spectively.
LISTEN TO this from the
High Powered Radio World's Fair: "'The
Frets Releases last frontier of radio re-
sistance will bow before this
final stroke of air-mastery, the automatic broad-
cast receiver,' said Rear Admiral Bradley Allen
Fiske, leading inventor of the United States
Navy for the past fifty years, as he declared
himself as being much interested in the automa-
tic broadcast receiver which was disclosed to the
press during the past week by Harry N. Marvin,
millionaire inventor of Rye, New York."
We hope Admiral Fiske didn't say any such
thing because the inventor of the torpedo plane
and the naval telescope sight which, again quot-
ing from the release, "has been adopted by all
the navies of the world and its use has been the
main cause of the improvement in accuracy of
modern naval gunnery," should know that
automatic tuning has been in use many years in
the navy, commercial, and amateur stations.
It is a simple matter to change the frequency
to which a station, or a receiver, is tuned by
pressing a button. How does the Admiral, or his
press agent, think the frequency of wcc, that
high-pressure coastal station of the Radiomarine
Corporation at Chatham Massachusetts is
changed? The operator is some miles away, and
while there is an attendant at the transmitter,
does he listen for a call on the 'phone, " Say bud-
dy, how's for tuning-up wcc to 2000 meters?"
We have been at Marion, Massachusetts, where
the transmitter is and have seen the thing in
operation. There is a click of a relay and the
signals go out on 2100 meters, another click and
the wavelength has been changed to 2000 meters,
another click and the transmitter is turned off.
No one has been near it for an hour or so.
No, the problem of turning on and off your
receiver, or of changing its frequency setting, or
regulating the volume control, all from a distance
is not new. Neither is the idea that in the navy
in time of war the frequency of a transmitter
could be changed rapidly and at the will of the
operator. Such schemes are as old as the appara-
tus itself and the business was reduced to prac-
tice many years ago.
If anyone wants to know how to tune his
radio by pushing a button instead of whirling a
knob, we'll tell him, and at the same time
give him data on how to turn the thing off
— in case of sopranos singing, for instance
— or to change the volume. As a matter of
fact, the interested reader may find an
article on such matters in this issue. This
scheme is at least old enough to have gone
through the patent office, and in these
days of radio inventions, this means some-
thing! Incidentally, Commander E. F.
McDonald of the Zenith Radio Corpora-
tion states that his company has acquired
Mr. Marvin's invention and that he, too,
believes the last frontier of radio will bow
etc., etc.
THE A. c. receiver
aA. C- seems to be causing
Troubles dealers and service
men no end of worry.
A dealer in New Hampshire writes us
typical complaint: "I. wish to state that
the a.c. tube sets around this section are
a decided failure. Fluctuating line volt-
ages ruin tubes in a few weeks. I know
of one individual that has had four sets
of tubes this winter. I spent an hour ex-
plaining why a.c. tubes were no good to
one prospective customer after which he
agreed with me and thanked me. How-
ever, the next day he promptly went
to my competitor and purchased an
a. c. set." —
We should like to point out that the
trouble is by no means altogether with
the a.c. tube. For example, we know an
editor of a nationally known magazine
who owns a Radiola 17 receiver. He lives
in a section of New York where line fluctua-
tions are very severe, so severe in fact that
he purchases a new 171 power tube and a.c.
tubes, too, about every two months. The trouble
here is patently not with the tubes, but with
the bad voltage regulation.
Any tube operated at a temperature above
normal will not last long. This means that a
tube whose manufacturer states should be oper-
ated at 2.5 volts cannot be expected to lead a
long or useful life if the voltage about half the
time is 3.0 volts. Tubes operated from a.c. will
last a long time if the voltage is normal or slightly
below.
From time to time we hear rumors of voltage
adjusting gadgets which are in process of
development; units that plug between the house
lighting socket and the receiver. Their duty is
to keep the voltage down to some fixed figure.
We predict a million dollar business for the first
reasonably priced and successful equipment of
this type.
60
100
200
500 1000
FREQUENCY
FIG. I
2000
5000 WPOO
84
RADIO BROADCAST
May Standard
Frequency
Signals
STANDARD FREQUENCY sig-
nals from the Bureau of
Standards have been used by
amateurs, laboratories and
experimenters for several years. These signals
are sent out about the 2oth of each month and
begin at 10:00 p. M. E. S. T. On May 21, signals
will be sent on frequencies of 650 to 1 500 kc. and
should serve as calibrating signals for wavemeters
and oscillators working in the broadcast range of
frequencies. The signals begin at 10:00 and con-
tinue until 1 1 :32 p. M. They consist of slightly
modulated c.w. telegraph and take place as
follows: at 10:00 a general call will be sent con-
sisting of the statement of the frequency, the call
letters of the Bureau station, wwv, then a series
of very long dashes and call signals on the stated
frequency, then the statement of the frequency
transmitted and the next frequency. These
signals require about 8 minutes, and are repeated
on the next frequency after a lapse of four min-
utes during which the transmitter is adjusted.
Anyone within 500 to 1000 miles of Washing-
ton, D. C. should be able to use the signals pro-
vided he has a receiver in which the detector can
be made to oscillate, a Roberts or Lab. Circuit,
for example. The receiver should be adjusted to
the approximate frequency, the detector oscillat-
ing, with a pair of receivers in the output of the
amplifier which may be one or two stages. At
the proper time, indicated below, the receiver
should be adjusted until wwv's signals are heard
beating with the oscillations of the local detector
circuit. This circuit should then be adjusted to
zero beat with wwv, and a wavemeter, preferably
an oscillating tube attached to a coil and con-
denser, is tuned also to zero beat. The wave-
meter and the receiver and wwv are then all
on the same frequency. A record should be kept
of the frequency and the setting of the wave-
meter condenser as well as that of the receiver
in case it is desired to calibrate the receiver. The
schedule follows:
KILOCYCLES
64,000 to 56,000
3, 5 50 to 3,500
2,000 to 1,715
METERS
4.69 to 5.35
84.5 to 85.7
i 50.0 to 175.0
E. S. T. MAY 21
10:00—10:08 P. M.
10:12—10:20
10:24—10:32
10:36—10:44
10:48—10:56
11:00—11:08
11:12—11:20
11:24—11:32
FREQU
650 ki
750
850
950
1060
1200
1350
1500
ENCY WAVELENGTH
462 metiers
400
353
316
283
250
222
200
GENERAL ORDER NO. 24 of
Short-Ware the Federal Radio Commis-
"Nfitt sion opens up a new telegraph
band for amateurs between
28,000 and 30,000 kilocycles, or 9.99 to 10.71
meters. It also defines an amateur station as one
"operated by a person interested in radio tech-
nique solely with a personal aim and without
pecuniary interest." It also makes slight revisions
in the telephone bands open to amateur traffic.
Radio telephones are now permitted to operate
in these bands:
NEW RCA AIRPLANE SET
On March 173 six-passenger Stinson-Detroiter
monoplane left Curtiss Field on a coast-to-coast
flight bearing five passengers and considerable
radio equipment. A photograph of some of this
apparatus, built by the R.C.A. is shown here. By
the time this appears, many amateurs will have
worked the plane whose radio gear was under the
key of H. C. Leuteritz, and which was licensed to
transmit on 120 meters using the call letters2XBK.
Attempts were made to get into contact with
the plane from the RADIO BROADCAST magazine
station, 2 GY, but by the time we got the receiver
wound up to operate on the rather unusual wave-
length of 120 meters, the plane was apparently
too far away. We heard several commercial sta-
tions calling her, and found a lot of interesting
things going on between 100 and 200 meters.
For example the coast guard boats using Western
Electric radio equipment could be heard all up
and down the coast hammering out information
about the rum fleet — probably. The stuff was in
code.
Not long ago we got up at 5 A. M. E. S. T. and
hammered out a CQ on our 4O-meter station,
2 EJ (See our April, 1927, issue). Two stations
came back at once, and on about the same fre-
quency, one fairly loud and the other quite weak.
We clicked with the louder of the two asking the
weaker to QRX for a few minutes. The louder sta-
tion turned out to be in Colorado and very glad
to be QSO the east coast because he was using
low power. After some conversation we signed
off and gave the weaker station a call, not know-
ing, of course, whether he was still standing-by
or not. Sure enough he came back, and he too
was most anxious to chat. He was using 180 volts
on a 1 12 type tube and had a call which indicated
he was in Oklahoma. A few days ago we received
a card from this operator stating that he was on
a boat in San Francisco harbor on the night in
question using about i watt input to his 1 12, and
not having a better one used his Oklahoma call.
The distance from San Francisco to Garden City
is something over 3000 miles which is not bad
for an input of i watt.
The following letter from M. W. Pilpel,
London, England, relates the success he has had
with a transmitter described in RADIO BROAD-
CAST. Mr. Pilpel's call letters are 6 PP and his
wavelength is about 45 meters. He states that
he is on the air every evening up to about 7 p. m
E. S. T. In this letter "NC" refers to a station
in Canada, "AQ" to Iraq, "AS" to Siberia and
"FM" to Morocco.
"I feel that I must write and tell about
the splendid results 1 have obtained with a
set described in your paper.
The set concerned is the " B Battery Trans-
mitter" described in your November, 1926,
issue. I built this set almost exactly as your
diagram, but used o.ooo3-mfd. condensers in-
stead of o.ooo25-mfd., and a grid leak var-
iable from 1500 to 100,000 ohms instead
of a fixed lo.ooo-ohm one.
The plate supply is
from accumulators,
180 volts, and the tube
used is a Marconi DE5,
more or less the Eng-
lish equivalent to your
ZOI-A. The antenna is
a small cage with four
wires and is only 1 5
feet long and 20 feet
high. The direct
ground is used.
Now for the results,
with an input of 27
m/a (4.8 watts) or less
I have succeeded in
JUNE, 1928
working four continents. Actually the best
distance worked is Manoa, Pennsylvania
where my friend NU-3PF gave me R2-3 during
a QSO lasting nearly ij hours. Two first dis-
trict NUs have also been worked. Then, NC
(R2-3), AQ (Ri!!) AS (R3), and FM (R6)
outside Europe. Only three European coun-
tries possessing hams have not been worked
yet, Rumania, Switzerland and Lithuania,
all others have been worked on more than
one occasion. LPJ at Spitzbergen gave me R3
in daylight, and OIK, when 400 miles south of
Greenland, R;. The best miles-per-watt is
over 900, ED 7HJ of Bornholm, Denmark, 750
miles away giving me R4 when using 0.8 watts.
I attribute these results chiefly to the
steadiness of the note emitted by the set and
must congratulate you on bringing this excel-
lent little "perker" to general notice and
describing it so well."
Recent Interesting
Contemporary
Articles
EACH MONTH we look
through the welter of radio
magazines and papers that
come into the office. Occasion-
ally, we read some of them. QST, for example,
disappears from the office the moment it comes
from the mail room and does not come back
until whoever took it has perused every word.
Then someone else grabs it. Experimental Wire-
less and Wireless Engineer (England) suffers the
same experience. The rest of them from a tech-
nician's standpoint, seem mediocre, a sad fact
true even of the Proceedings of the I. R. E. at
times. The following recent articles are worth
reading.
TITLE MAGAZINE DATE
Double Detection Detectors
and Screen-Grid Amplifiers QST March
Directional Properties of An-
tennas QST March
The Photoelectric Cell Radio February
Frequency Stabilization on
Short Waves by Quartz
Crystals L'Onde Electrique January
Theory of the Antenna Wireless Exper-
imenter March
A Radio-Frequency Oscillator /. R. E. February
Theory of Power Amplification I. R. E. February
Ideals of the Engineer
by John J. Carty Journal,
A. 1. E. E. March
Use of Very High Voltage in
Vacuum Tubes by W. D.
Coolidge journal,
A. 1. E. E. March
IN SPITE of the fact that
Another Useful OUT friend C. T. Burke of the
Publication General Radio Experimenter
catches us up, publicly,
whenever we make a mistake, we still believe
that every serious radio thinker should be on the
list of those getting this excellent trade publica-
tion.
A similar sheet has arrived in the Laboratory.
It is called the Aerovox Research Worker and is
published by the Aerovox Wireless Corporation,
70 Washington Street, Brooklyn, New York.
It, too, is worth having regularly. In our list of
"Manufacturers' Booklets Available," regularly
listed in the back advertising pages of this
magazine this publication is listed as No. 120.
ANYONE WANTING a free
Radio School ticket to the Radio Institute
Scholarships of America should get in
touch with J. V. Maresca,
Room 1889, Hotel Roosevelt, New York. He
has charge of applications for two scholarships
offered by the Veteran Wireless Operators'
Association and the two offered by A. H. Grebe.
Awards will be made to those American born
youths over eighteen years of age who write the
best letters of essays on "Why the American
Merchant Marine Needs Perfect Wireless Com-
munication."
— KEITH HENNEY.
New Apparatus
An Inside Antenna
Device: INDOOR AERIAL. Consists of a seventy-
foot spool of indoor aerial wire, a twenty-five foot
length of rubber-covered ground wire, and a
ground clamp. The aerial wire is made of
stranded copper covered with a brown braid.
Manufactured by the BELDEN MANUFACTURING
COMPANY. Price: $1.55.
Application: Designed especially for indoor
antennas, the wire is flexible and can be easily
wired around a room, over window frames, and
because of the neutral brown color of the braid,
the wire is practically invisible.
Fine New Drum Dial
Xji
Device: NATIONAL TYPE F VELVET VERNIER
DRUM DIAL. Dial light is readily removable,
and has both terminals insulated from the dial.
Dial numbers are engraved on strip. Drum is
made of brass, with nickel plating and the dial
front is silver plated. The movement has
NATIONAL DRUM DIAL
absolutely no back-lash. Manufactured by THE
NATIONAL COMPANY. Price: $4.50.
Application: May be used in constructing any
receiver. One of the best drum dials that have
been received in the laboratory.
A Good Phonograph Pick-U-p
X32
Device: Amplion Phonograph Pick-Up Unit.
Device is complete with tone arm and volume
control. Manufactured by the AMPLION COM-
PANY. Price: $15.00.
Application: To be used in conjunction with a
phonograph turn-table and an audio amplifier
to make possible the electrical reproduction of
phonograph records. The tone arm is screwed
down on the turn-table bed of the phonograph in
such a position that the unit on the end of the
tone arm can be correctly placed on a record.
The Laboratory's sample of this pick-up has
given very satisfactory reproduction of records
and it has the advantage over some other pick-
ups that it exerts but slight pressure on the rec-
ord resulting in less record wear.
Resistor for the Screen-Grid Tube
*33
Device: AMPERITE No. 622. Filament-control
resistance for screen-grid tubes. When placed in
series with the tube filament and a six-volt
battery, this resistance will reduce the voltage to
3.3 volts, the correct voltage for a screen-grid
tube. Manufactured by the RADIALL Co. Price:
$1.10.
Application: May be used for filament control
of the screen-grid type tubes in a receiver.
Amperites for each type of tube are made.
Complete data on the different styles available
may be obtained by writing the manufacturer
through RADIO BROADCAST.
Set Tester of Wide Use
X34
Dei-ice: RADIO SET TESTER, A. C AND D. C.
MODEL 537. This set tester is designed for the
testing of all kinds of radio receivers operated
from either alternating or direct current light
socket power or from batteries. It will measure
the various voltages used in the radio set both
at the tube sockets or at any part of the set; it
will test continuity of circuits, and test the tubes
under the same conditions as exists when in their
sockets. All tests can be made by using the volt-
ages normally supplied to the set by its batteries
or socket power with no change in connections,
so that no auxiliary power supply is required.
Socket adapters are supplied so that uv, ux
and UY type tubes may be tested.
All of these tests are possible using the two
meters contained in the instrument, which are an
a. c. voltmeter having three ranges 150, 8, and 4
volts, and a d. c. volt-milliammeter which has
four voltage ranges, (600, 300, 60, and 8 volts)
and two current ranges, (150 and 30 milliam-
peres). The voltmeter has a resistance of 1000
AMPLION PHONOGRAPH PICK-UP
ohms per volt and can therefore be used satis-
factorily to measure the output voltages of B
power units. Tests on tubes can also be made
independent of any radio receiver by connect-
ing a plug supplied with the instrument into a
light socket.
r) ROpUCTS of radio manufacturers whether
1 new or old are always interesting to our
readers. These pages, a feature of RADIO BROADCAST
explain and illustrate products which have been
selected for publication because of their special
interest to our readers. This information is pre-
pared by the Technical Staff and is in a form which
we believe will be most useful. We have, wherever
possible, suggested special uses for the device men-
tioned. It is of course not possible to include all
the information about each device which is avail-
able. Each description bears a serial number
and if you desire additional information direct
from the manufacturer concerned, please address a
letter to the Service Department, RADIO BROAD-
CAST, Garden City, New York, referring to the
serial numbers of the devices which interest you
and we shall see that your request is promptly
handled. — THE EDITOR.
Manufactured by the WESTON ELECTRICAL
INSTRUMENT CORP. Price: Sioo.
Application: An essential instrument for the
radio dealer and the professional radio service
man, for it makes possible the thorough, accurate
and rapid testing of a receiver.
For the 250 Type Tube
.
Device: Power Equipment for the 250 type tube.
The apparatus listed below has been designed
for the 250 type tube. This tube requires much
more plate current than other types of power
amplifier tubes and therefore the apparatus for
use with it must be constructed to prevent
overheating and saturation effects at high
currents.
TYPE 565-6 FULL-WAVE TRANSFORMER.
Designed for full-wave rectrfication using two
type 281 tubes. The plate voltage winding is
1 200 volts with a center tap. There are also two
WESTON SET TESTER
7-5-volt secondaries for the filaments of the
rectifier and power amplifier tubes. Price : $20.00.
TYPE 565-A HALF-WAVE TRANSFORMER. This
transformer is designed for half-wave rectifica-
tion in conjunction with one 281 type tube.
There are four secondaries: one of 600 volts for
the plate voltage; two of 7.5 volts each for the
filaments of a rectifier and power amplifier tubes;
and one of 2.5 volts for the filaments of 226 and
227 type of tubes in case this transformer is in-
corporated in a complete two- or three-stage
amplifier. Rated at 200 watts. Price: $20.00.
TYPE 5&7-A SPEAKER FILTER. A speaker
filter that thoroughly insulates the speaker
from the high plate voltage and current of the
last-stage tube. The choke used is of unusually
heavy construction and has an inductance of
approximately 15 henries and a continuous cur-
rent rating of 100 milliamperes. The direct cur-
rent resistance is 250 ohms. Two microfarad
condensers are used on each side to completely
insulate the speaker from high voltage. Connec-
tions to the input side are in the form of leads
while the speaker is connected to two binding
posts. Price: $10.00.
TYPE 527-A RECTIFIER FILTER. This unit
consists of a combination of two heavy-duty
chokes with an inductance of approximately 13
henries each and a continuous current rating
of 100 milliamperes and a condenser assembly
consisting of a 4-2-4~mfd. combination rated
at 1000 volts d. c. The direct current resistance
of each choke is 175 ohms. Price: $25.00.
All the above apparatus Manufactured by the
GENERAL RADIO COMPANY.
Application: This apparatus may be used in
86
RADIO BROADCAST
JUNE, 1928
constructing power amplifiers using the 250 type
tube especially, although the equipment is of
course suited to the construction of any power
unit from which it is desired to obtain compara-
tively large amounts of current, say 60 milliam-
peres or more.
Dynamic Speaker Models
Device: JENSEN DYNAMIC SPEAKER: A moving-
coil type loud speaker. It may be connected
directly to the output of a receiver without any
need of an output device, for the transformer
contained within the loud speaker insulates the
windings of the moving coil from the plate cur-
rent of the power tube. The field winding of the
speaker must be supplied with energy from an A
battery (Model D-44), or from a go-volt d. c.
source (Model 0-45) or from the I lo-volt a. c.
mains (Model 0-44. a. c.). Manufactured by
the JENSEN RADIO MFG. Co.
Price: Model 0-44, $65.00; Model 0-45, $67.50;
Model D-44-AC. $75.00.
Application: A sample of this loud speaker has
been in use in the Laboratory for some time and
has proved to be an excellent instrument. An
elementary diagram of the loud speaker appears
Intense magnetic
Circular paper cone
specially treated '•••
Field connections to
storage A Battery
D.C.6Volts-0.4Amp.
or A C.6 Volts, rectified
and filtered
>• 8H depth overall
DIAGRAM OF JENSEN CONE
herewith. The cross-sectioned part represents a
magnet, energized by the current flowing through
the field winding. As a result there is produced
across the gap in the magnet an intense magnetic
field. The paper cone is arranged as indicated,
projecting into the gap, and around this portion
of the cone is wound a small coil of wire. This
coil is connected to the secondary of the step-
down transformer, the primary of which con-
nects to the output of the radio receiver. The
signal currents flowing through the coil react
with the magnetic lines of force flowing across
the gap and produce a torque which makes the
coil move left and right. The cone, attached
solidly to the moving coil, must also move with
the coil and its movements produce the sounds.
This loud speaker gives best results when
operated in conjunction with a large baffle but
will also work very well in the cabinet supplied
(F)
CIRCUITS FOR CENTRALAB VOLUME CONTROLS
by the Jensen Company. The cone unit can also
be purchased without the cabinet for installa-
tion in radio or phonograph consoles.
Resistors for A. C. Sets
X37
Device: VOLUME CONTROL RESISTANCES, for
a. c. receivers. The method of volume control
commonly used in d. c.-operated receivers, i. e., a
filament rheostat in the filament circuit of the
r. f. tubes, cannot be applied to a. c. circuits
because lowering the filament potential of 226
type tubes will tend to produce a hum in the
loud speaker and because with 227 type tubes
the emission from the heater will lag behind
changes in the current through the heater fila-
ment. It is therefore necessary to use some other
type of volume control. The devices listed below
will be found very satisfactory.
RX-ioo Radiohm, a special tapered resistance
for use across the secondary of one of the r. f.
transformers, preferably the detector stage. See
Fig. I -A. Price; $2.00.
RX-O25 Radiohm, a special tapered resist-
ance for use as a volume control across the
primary of an r. f. transformer or across the
primary of a tuned antenna coil. See Fig. i-B.
Price: $2.00.
P-H2 Potentiometer. A 6ooo-ohm potentiom-
eter with a special tapered resistance at the
end to be used in the antenna circuit or across
the primary of a tuned r. f. stage. See Fig. i-C.
Price: $2.00.
M-5oo Modulator. A potentiometer with a
special tapered resistance for the grid circuit
of one of the audio stages. Used principally as an
auxiliary control in a. c. circuits. See Fig. i-D.
Price: 2.00.
HP-O5O Heavy Duty Potentiometer. A wire-
wound, non-inductive potentiometer used as a
plate circuit control. See Fig. i-E. Pricf: $2.00.
PR-O5O Power Rheostat. A specially con-
structed rheostat to carry heavy currents and an
excellent control for use in the primary of a
power transformer. See Fig. i-F. Price: $1.25.
All of the above units are manufactured by the
CENTRAL RADIO LABORATORIES.
Application; The application of these units to
a. c. circuits has been covered in the data given
above. A useful pamphlet is obtainable from the
manufacturers through RADIO BROADCAST de-
scribing these units in detail and giving further
information regarding the circuits in which they
are to be used.
TRUVOLT RESISTORS AND BELDEN ANTENNA KIT
JENSEN DYNAMIC CONE
Resistors for Power Supply Use
X38
Device: TRUVOLT RESISTORS. Wire-wound resis-
tors, using Nichrome wire wound on an asbestos
covered enamel core. Available as fixed and
variable resistors as follows:
TYPE T, variable resistors, with maximum
resistances of 200 to 50,000 ohms.
TYPE B, fixed resistors, rated at 25 watts,
and available in sizes from 200 to 50,000 ohms.
TYPE C, fixed resistors, rated at 50 watts,
and available in sizes from 200 to 100,000 ohms.
TYPE D, fixed resistors, rated at 75 watts,
and available in sizes from 200 to 100,000 ohms.
TYPE V, center-tapped fixed resistors, available
in sizes from 10 to 200 ohms, and designed es-
pecially for use as center-tapped resistors across
the filaments of a. c. tubes.
GRID RESISTORS, available in sizes from 10
to 2000 ohms, and designed especially for use as
grid suppressors, in radio-frequency amplifiers.
SPECIAL TAPPED FIXED RESISTORS, designed
for use with the popular types of power packs
such as those made by Silver-Marshall, Amer-
tran, Samson, Thordarson, etc.
Manujactured by ELECTRAD, INC. Prices: vary
according to the style and rating of resistors.
Application: The Truvolt line of resistors is very
complete and units are available to meet almost
every need in the construction of radio receivers
and power packs. Complete data can be ob-
tained from the manufacturer through RADIO
BROADCAST.
LIFE FOR A WEAK RECEIVER
The screen-grid tube can be added to any receiver, and — at the cost of one
additional control— will add a respectable amount of sensitivity and
some selectivity. Directions are given for using this unit with any receiver
A Screen-Qrid Booster Unit for Any Receiver
THE introduction of the screen-grid tube
has opened a new field in r.f. amplification,
for not only does this tube make possible
at broadcast frequencies an amplification much
greater than is possible with a 2OI-A type, but
because of its very small capacity between con-
trol grid and plate, relative stability as an r.f.
amplifier is secured.
As most experimenters know, the screen-grid
tube has two grids, one forming a nearly complete
shield around the plate and known as the screen
grid, while the other is practically the same as
the grid in the ordinary tube, and is called the
control grid. The screen-grid has two effects; it
shields the plate as its name indicates, and also
increases the mutual conductance in such a
manner that the amplification of the tube may
be at some frequencies as high as 100. The func-
tion of the control grid is, as in the 2OI-A tube,
to regulate the flow of electrons between fila-
ment and plate.
The construction of the tube may be seen in
the accompanying photographs. The metal cap
on top of the tube is the terminal for the control
grid while the prong on the socket, marked
"grid," is the terminal for the screen-grid. These
connections should be carefully noted.
By Glenn H. Browning
Browning-Drake Corporation
To get the utmost from the screen-grid tube
involves careful shielding of the tube and the
circuit in which it is used. There are thousands
of sets which are not now shielded nor could they
readily be shielded. This difficulty, in addition
R. BROWNING'S "booster" provides at one
time a means of improving the TJX ability
of any receiver and its selectivity. In the Laboratory,
it was possible to hear stations that were not audible
without it. It was also possible here to listen to KDKA
with very little interference from WABC, only 8
miles away, while under usual conditions this is not
•possible at all. In our estimation, this booster should
be a gold mine to service men — because nearly every
one wants some little gadget like this that will make
an otherwise almost-dead receiver come to life.
We hope that Mr. Browning will design a set
of plug-in coils so that this single stage of r.f.
amplification may be used with short-wave receivers.
It will then eliminate nearly all radiation from
these receivers, as well as improve signal strength.
— THE EDITOR.
to the fact that it is very rare indeed that any
existing circuit can be efficiently and easily al-
tered for the successful use of the screen-grid
tube makes it wiser in most cases to find ways
of utilizing the high gain to be secured from the
screen-grid tube elsewhere than in the receiver
proper.
For the last year there has been an insistent
demand for another stage of tuned radio-
frequency amplification to be added to the
Browning-Drake receivers. The writer has
worked a great deal on this problem only to come
to the conclusion that it was not feasible for the
home-builder because of the high gain in the
Browning-Drake transformers which entails
careful construction, and critical adjustment of
the neutralizing condensers. However, with the
availability of the screen-grid tube, the problem
simplifies itself considerably.
For some time the writer has been experiment-
ing with a one-stage r.f. amplifier which could
be added to the large number of Browning-Drake
sets which are in use. This amplifier employs
the screen-grid tube, and not only gives a tre-
mendous r.f. amplification, but increases selec-
tivity to a marked degree. It has also been
found that the one-stage amplifier can be used
RADIO BROADCAST
JUNE, 1928
B-M5
Leave ground
connected to Receiver
Ant. on Set
of Receiver
O
B+90
CIRCUIT OF THE BOOSTER UNIT
The antenna connection indicated will work with all Browning-Drake type receivers •
with others, it is best to connect the antenna lead to the set directly to the stator
plates of the first tuning condenser
not only on Browning-Drake sets, but on any
existing receiver, simply by making a connection
to the stator plates of the first tuning condenser.
[The lead from the "booster" may be connected
to the antenna posts of some receivers, but not
all, and it is best to follow the suggestion here
which is certain to work. — EDITOR.] By using this
one-stage device, the writer has received signals
that were inaudible before.
The assembly of the one stage screen-grid
booster is quite simple. The Browning-Drake
Corporation furnishes a kit consisting of the
coil, condenser and dial, together with a set of
aluminum shields, a radio-frequency choke, a
four-wire cable, lo-ohm resistances and the
mounting hardware, and all that is necessary for
the constructor to purchase is a tube socket, and
the three following condensers; a j mfd., a o.oooi
mfd. and a 0.00025 mfd.
The picture wiring diagram and the schematic
wiring diagram are presented on this page. It
should be noted that the stator plates of the
tuning condenser go to the top of the screen-grid
tube. The two lo-ohm resistances, put in as in-
dicated, cut down the six volts from the storage
battery to 3.3 volts which is the correct voltage
for the screen-grid. It is noted that the one-stage
booster is run from a battery as the writer does
not believe it feasible to light the filament of the
cx-322 from raw a.c. In using the one-stage
booster on any Browning-Drake assembly, all
that is necessary to do is to disconnect the an-
tenna from the set, connect it to the antenna post
of the booster, which is shown on the left, and
to connect the wire lead, which is on the right
of the booster to the antenna post on the
Browning-Drake receiver. The ground is left in
its position on the set proper. From the wiring
diagrams, it may be noted that a filament switch
is inserted in the pIus-A battery lead to control
the filament of the cx-322 tube. This makes the
separate amplifier unit independent of the re-
ceiving set proper and permits it to be used on
any radio set. When using the booster on
Browning-Drake receivers, particular care should
be taken that the set is well neutralized before
adding the booster. Volume may be controlled
as before on the receiving set.
HOW TO CONNECT THE BOOSTER
VA/HEN using this one-stage booster with
* other receivers, the wire on the right of
the shield casing, is connected to the stator
plates on the first tuning condenser. The other
connections are unchanged, except that the
antenna lead is connected to the proper post on
the booster. The operation of the booster is very
simple indeed as all that is necessary to do is to
tune-in the receiver by means of the regular
control and then tune the booster.
Tuning on the booster unit is not extremely
critical though it increases the selectivity of the
set in a marked degree. The antenna used on the
receiver when this booster is employed should
be very short, in fact, not more than 25 to 40
feet, and as nearly vertical as possible. The
vertical antenna will pick up relatively a
stronger signal.
LIST OF PARTS
i Browning-Drake Booster 322 Kit assembly.
(Includes shields, the coil and tuning
condenser with dial, two lo-ohm resist-
ances, a four-wire cable, shield wire, and
r.f. choke).
i ux tube socket.
I o.oooi-mfd. mica Condenser.
i j-mfd. mica Condenser.
i o.ooo25-mfd. Condenser.
00025 mfd
To Antenna
on Set
A PICTURE DIAGRAM
How to connect the various parts em-
ployed and the recommended layout
. .
Our Readers Suggest
9 9
OUR Readers Suggest" is a clearing house
for short radio articles. There are many
interesting ideas germane to the science of radio
transmission and reception that can be made clear
in a concise exposition, and it is to these abbrevi-
ated notes that this department is dedicated. While
many of these contributions are from the pens of
professional writers and engineers, we particularly
solicit short manuscripts from the average reader
describing the various "kinks," radio short cuts,
and economies that he necessarily runs across from
time to time. A glance over this "Our Readers Sug-
gest" will indicate the material that is acceptable.
Possible ways of improving commercial appara-
tus is of interest to all readers, The application of
the baffle board to cone loud speakers, is a good
example of this sort of article. Economy "kinks,"
such as the spark-plug lightning arrester, are most
acceptable. And the Editor will always be glad to
receive material designed to interest the experi-
mental fan.
Photographs are especially desirable and will be
paid for. Material accepted will be paid for on pub-
lication at our usual rates with extra consideration
for particularly meritorious ideas.
— THE EDITOR.
An Emergency Detector B Supply
IT HAS been my experience that the voltage
distributing resistor system in the average B-
power unit is the weak point of these devices.
On several occasions the resistor passing the
current to the detector tube in my receiver has
gone bad. I found that an emergency connection
could be effected in a few seconds, by wiring an
outside resistor from the "detector B" post on
the set to the "amplifier B" post on the unit.
A ioo,ooo-ohm resistor is about the correct
value. The set works quite as well operating the
detector tube from the 90 volts power-unit tap,
through the external resistor, as it did from the
original "detector B" supply post.
I rigged up the resistor mounting, shown in
Fig I, to enable me to try different values of
resistors. The mounting is wired, as shown, to
the "amplifier B" positive post, and the detector
lead is caught under the Fahnestock clip.
PERRY WHITE. New York City.
STAFF COMMENT
j N SOM E cases it may be desirable to bypass
* this extra resistor. This can generally be ac-
complished by leaving the lead to the "detector
B" post on the set (now wired to the special re-
sistor) also connected to the original "detector
B " supply post on the power unit, taking advan-
tage of the bypass condenser included in that
circuit. As the faulty resistor is probably " open "
this will have no effect on the potential. If de-
sired, the resistor may be bypassed by connecting
any convenient condenser from i.o mfd. up.
across the resistor. It is also possible to connect
the external resistor directly across the "am-
plifier B" plus and the "detector B" plus posts
on the receiver itself, without going back to the
power supply unit.
The clip-wired Clarostat and the clip-wired
FIG. 1
This simple arrangement can be used to supply
either detector or intermediate-amplifier plate
potential from a high voltage tap in the case
of resistor break-down.
FIG. 2
The use of clip connectors permanently fastened
to flexible leads for condensers and resistors
greatly facilitates experimental and emergency
work for many uses around the radio set
bypass condensers suggested by Mr. Graham,
elsewhere in this department, are particularly
convenient in effecting temporary arrangements
of this kind.
Emergency and' Experimental
Connections
IN MY experimental work, as well as in emer-
* gency set-ups in the perpetual endeavor to
keep the family set functioning properly, I have
found it very convenient to have a complete set
of parts available for immediate connection by
means of clips. The idea, illustrated by a few of
the parts so arranged, is made clear in the accom-
panying photograph (Fig. 2.).
The clips used are of the small battery type,
obtainable at most electrical afid radio supply
houses. Any type of ordinary hook-up wire may
be used for the leads — I used flexible Celatsite.
In the cases of certain parts, such as the con-
densers which already have long and flexible
leads, these may be soldered directly to the clips.
The following parts which I happened to have
on hand, were arranged with two-foot leads and
clips:
I Volume control Clarostat (variable re-
sistor)
89
i Universal range Clarostat (variable re-
sistor)
i Low range Clarostat (variable resistor)
I Amsco 2ooo-ohm Duostat
1 40O-ohm potentiometer
2 Fixed condensers, o.ooi mfd.
1 Gridleak mounting
2 Bypass condensers with leads, o. i mfd.
3 Filter condensers with leads, 4.0 mfd.
i looo-ohm fixed resistor
i 25OO-ohm fixed resistor
i 5000-ohm fixed resistor
i io,ooo-ohm fixed resistor
3 6o-ohm center-tapped resistors
It is also a good idea to have on hand a half
dozen or so three-foot lengths of flexible wire
with clips on the ends. The above parts arranged
for instant clip connections, will be more than
handy in all experimental work.
HERBERT GRAHAM, Chicago, Illinois
Volume Control for Resistance-
Coupled Amplifiers
COME receivers, particularly sets using a.c.
^ tubes, employ a type of volume control such
that the signal cannot be reduced without im-
pairing selectivity to a serious extent. This con-
sideration justifies the control of volume at a
point in the circuit following the detector tube
where it will have no effect on selectivity. Some
circuits employ a high resistance potentiometer
across the secondary of the first audio transfor-
mer in a transformer-coupled amplifier.
When using a resistance-coupled amplifier a
somewhat similar arrangement can be used, and
is suggested in Fig. 3. The coupling resistor in
the detector plate circuit is a high range potentio-
meter (.1 to .25 megohms maximum) such as the
Electrad Royalty, with the movable arm con-
nected to the coupling condenser.
This arrangement provides adequate volume
control without changing the frequency charac-
teristic of the amplifier.
H. F. KUCKS, New York City.
STAFF COMMENT
A S MR. KUCKS points out there are certain
** types of volume controls which impair the
selectivity, as for example a variable resistance
across the primary or secondary of an r. f. trans-
former. Such difficulties can be prevented by
FIG. 3
A volume control circuit for use
with resistance-coupled amplifiers
90
•RADIO BROADCAST
JUNE, 1928
placing the volume control in the audio amplifier
but this control has the disadvantage that it will
not prevent the detector overloading on strong
signals. There are several satisfactory volume
controls that can be applied to a.c. receivers
which will not affect the selectivity and which
will also prevent detector overloading on strong
signals. We mention two types.
One fairly good control is a variable resistance
connected in series with the B-plus lead to the
primaries of the r. f. transformers. This resistance
should have a maximum value of about 200,000
ohms and a o.i-mfd. or larger bypass condenser
should be connected across it. As the amount of
resistance in the circuit is increased, the effective
voltage applied to the plates of the r. f. is lowered
and the volume is thereby decreased. Such a
control will not impair the selectivity, but, with
some receivers will cause an undesirable in-
crease in voltage applied to the other tubes
in the set.
A simple type of volume control that may
generally be used merely consists of a variable
resistance connected between the antenna and
ground posts on the set. The resistance should
have a maximum value of about 50,000 ohms.
Centralab, Yaxley, and others make a special
resistance for this purpose.
Some Baffle Board Experiments
STAFF COMMENT
THE baffle board consists of a reflecting sur-
face applied near a cone speaker. In many
cases this takes the form of a large box, in which
the cone is placed. In others it is a short horn
having a relatively large bell, the cone being
used as a diaphragm. In many instances, the
use of baffle boards will improve reproduction of
the low frequencies especially. As experimental
boards are easily constructed, they are worth
trying.
The two following contributions consider the
possibilities of the use of baffles.
FIG. 4
A baffle arrangement with a 540 AW cone speaker
0.00025
mid.
FIG. 5
An antenna tuning circuit for use with neutro-
dynes and other receivers having an untuned
primary circuit
IN EXPERIMENTING with a Western Elec-
* trie 540 AW cone I found it possible to attain
a marked improvement in the reproduction of
the lower audio frequencies, without apparent
impairment of the higher notes through the use
of a baffle board. The accompanying photograph,
Fig. 4, illustrates the baffle arrangement em-
ployed by the writer.
I made a 36 by 36-inch wood frame, 12 inches
deep. The front was faced with heavy roofing
paper, with a circular hole, eighteen inches in
diameter, cut out in the center. The cone was
placed in this cabinet with the face of the cone
brought as close to the opening as the frame of
the loud speaker would permit. The assembly
was then mounted on top of the chest of drawers
as shown in the photograph, and placed in the
corner of the room so that the sides of the en-
closing cabinet touched the walls. By so doing
the baffle effect of the sides was greatly increased,
and the supporting furniture also functioned as
part of the baffle.
The power tube used is a ux-iyi outputting
to the speaker through a loo-henry choke coil
and a g.o-mfd. condenser. This tube outputs ade-
quate distortionless power to the baffled loud
speaker with 135 volts on the plate.
A slight barrel effect in
speech was counteracted by
placing a piece of heavy cloth
on the back of the cabinet,
thus avoiding sound reflec-
tion.
PAUL S. FOSTER, New
York City.
A CAREFUL considera-
•" tion of the most effective
method of mounting a free-
edge baffle type cone speaker
is necessary if the best results
are to be secured. Fairly good
results can be expected by
using a flat baffleboard of
sufficient thickness and rigid-
ity to be nonresonant
throughout the audio range.
A deep cabinet or console,
however, will tend to improve
the lower frequency response
of the speaker by allowing a
greater effective baffling area.
The greater the baffling
area the better will be the
reproduction of the low
notes.
Deep box baffles of the
type to which we have refer-
ence often give rise to a
resonance effect within the
audio range, resulting in the
exaggeration of certain fre-
quencies, noticeable as a
booming sound or barrel tone. One method of
correcting this condition is to vent the baffle
by cutting holes or louvres in the sides of the
console. This has the disadvantage of reducing
" the effective baffling area and often impairs the
appearance of what otherwise would be a hand-
some bit of furniture. At best my present sugges-
tion is a trial and error method.
In mounting a free-edge cone in a baffling
arrangement of this type, the writer finds that
resonance can be completely eliminated by lining
the interior with felt. Felt packing of a thickness
of j inch was used, although a somewhat thinner
lining would probably have worked just as well.
The entire interior of the cabinet, was lined with
the packing and secured by glue and tacks.
D. C. REDGRAVE, Norfolk, Virginia.
Antenna Tuning Device
T^HE apparatus described below- is an indis-
* pensable portion of my receiver equipment for
distant reception. Many broadcast fans, located
like myself at some distance from broadcast
centers, will find this simple device of use to
them.
On many evenings, when stations two hundred
to three hundred miles away are practically in-
audible, a variometer and two variable conden-
sers, connected as shown in Fig. 5 boost the vol-
ume from ten to twenty times, often making
enjoyable loud speaker reception possible. The
device does not change the original dial settings
of the receiver. Once the variable condensers are
set to the proper capacity (to be determined ex-
perimentally) they need not be touched again,
all tuning being effected on the variometer.
However, the o.ooo25-mfd. variable is very
effective as a volume control. This apparatus is
not effective on all receivers, but is designed
primarily for use with sets having untuned an-
tenna primaries, such as the average neutrodyne
and tuned r.f. receiver.
A. GAUDETTE, Lewiston, Indiana.
STAFF COMMENT
*~pHE arrangement described -above is an an-
*• tenna tuning device. The control described
by Mr. Gaudette is really a combined antenna
tuning device and a wave trap. In the majority
of instances it can be simplified to the circuit
shown in Fig. 6. Coil L may be the secondary
of any available radio-frequency amplifying
transformer, or sixty turns of wire wound on a
three-inch diameter form. This device will be
most effective on short indoor antennas.
A Spark Plug Lightning Arrester
j_I ERE is a simple and effective lightning ar-
' rester. It consists of a good heavy spark
plug, and a piece of pipe, three or four feet long,
into which the plug can be screwed.
The pipe is driven into the ground and the
spark plug screwed into it. The ground connec-
tion is automatically taken care of. The wire
from the antenna is led to the binding post on
top of the spark plug and from there to the re-
ceiver. That is all there is to it.
GEORGE KOETHER, JR., Round Bay, Maryland.
\
7
Hi
/
k To Ant Post
<O< on Set
•1
0.0005
§j FIG. 6
mfd. .
CZX A simplified version of
•
<O\ Fig. 5. Both Fig. 5 and
<^j Fig. 6 are most effec-
S five when used with
short antennas
JUNE, 1928
RADIO BROADCAST
91
No. 1.
June, 1928.
RADIO BROADCAST'S Service Data Sheets on Manufactured Receivers
The Amrad A. C. 7
THE Amrad A. C. 7 is another representative
of the a.c. electric receiver of the neutrodyne
type. This receiver utilizes seven tubes, six
of which are of the a.c, type while the seventh is a
171. A study of the wiring diagram of the complete
receiver installation will bring to light several novel
features in design. There are four stages of radio-
frequency amplification, a non-regenerative de-
tector, and two stages of transformer-coupled audio-
frequency amplification. The power is obtained
from a full-wave B power unit which simultane-
ously supplies the B voltage for the plates of the
tubes and the a.c. voltages for the filaments.
The r.f. system consists of an antenna coupling
stage and three stages of Hazeltine-neutralized
tuned radio- frequency amplification. The receiver
is designed for a short antenna and the first r.f.
stage is really a coupling stage, being untuned. The
input circuit of this coupling tube consists of a
radio- frequency choke, tapped for the antenna, in
series with a fixed resistance, which is grounded.
By utilizing this coupling tube the tuned settings
of the other three stages are not disturbed by
variations in antenna length or capacity. A very
novel method of volume control for the entire re-
ceiver installation is incorporated in the plate cir-
cuit of this coupling tube. It consists of a variable
• resistance connected across the bifilar primary
winding. Under normal circumstances a volume-
control of this type would manifest an effect upon
the grid circuit of the average tuned stage but since
the grid circuit of this tube is untuned the effect
of this variable resistance is that of only a volume
control, without any detrimental effects upon other
circuits. Each of the r.f. stages is contained in a
separate can. The audio stages are not shielded and
are of the conventional type, with an output trans-
former utilized to couple the loud speaker to the
output tube.
All four stages of radio-frequency amplification
are neutralized, and the neutralizing condensers
are designated as C? in the wiring diagram. The
bifilar primaries utilized in this system of neutrali-
Coupling Tube 1st R.F
"
zation are marked Li in the drawing. The'receiver
is a single-control unit, the four tuning condensers
being ganged together and operated from one point.
A filter system, consisting of a resistance and a
capacity, is incorporated into the detector plate
circuit, probably to keep the a.c. hum at a low
value. The plate voltages for the r.f. tubes and
the detector are obtained from one tap on the
power unit, but voltage-reducing resistances lo-
cated in the plate circuit of each radio-frequency
THE SET IN ITS CABINET
tube and in the plate circuit of the detector tube,
reduce this voltage to the correct values for the
individual tubes. It should be understood that
volume control in this installation is not accom-
plished by plate-voltage reduction. At first glance
one would assume this to be the case. Volume-
control is obtained by a resistance which varies
the a .c . yol tage across the first-radio-frequency
primary winding. Bypass condensers are used to by-
pass the filament and plate circuit in every stage:
to further facilitate receiver stability, a radio-
frequency choke is wired into the plate-voltage
system in the r.f. circuit.
As was stated, the filament circuits are all a.c.;
and electrical balance is obtained by means of po-
tentiometers. These are designated as Pi, P2l and
Ps in the wiring diagram. The grid bias for the vari-
ous -tubes is obtained by means of a resistance
through which the plate current flows and results
in a predetermined voltage drop. These voltage-
drop resistances are marked Rj and RB. As is evi-
dent from the drawing, the grid bias voltage is of
like value for the r.fT and the first audio tube,
while individual grid bias is obtained for the out-
put tube.
The power unit is of conventional type with two-
variations. The rectifying tube is of the 280 full-
wave type. As a contrast to other filter systems em-
ployed in rectifiers, this installation utilizes but one
filter choke. The required filtering action is ob-
tained by the use of large values of capacity. A
Mershqn condenser of several sections (each sec-
tion being of relatively high capacity) is employed.
As is evident in the wiring diagram, two sections of
this condenser are connected across taps of the
voltage distributing resistance. This aids materi-
ally in the lowering of the effective resistance of the
output circuit, and in the reduction of regenera-
tion due to the action of this resistance as an im-
pedance common to all circuits. The power trans-
former utilized consists of six windings. The pri-
mary winding is tapped for three values of line
voltage. One secondary winding supplies the fila-
ment voltage for the rectifying tube, another
supplies the plate voltage for this tube. The other
three supply the a.c. filament voltages necessary
for the various tubes in the receiver. Since a shunt
potentiometer method of obtaining electrical bal-
ance is utilized, center taps on the a.c. filament
windings are unnecessary. Control of the complete
receiver is accomplished by means of a switch in
series with the house supply circuit and the trans-
former primary. This switch is located on the face
of the receiver panel.
2.5 Volts White
*v^~v'~V — V
^X^^A— *^_ •*• __
k& Yellow 5 Volts
THE CIRCUIT DIAGRAM OF THE AMRAD A. C. 7
92
RADIO BROADCAST
JUNE, 1928
No. 2.
June, 1928.
RADIO BROADCAST'S Service Data Sheets on Manufactured Receivers
The Pfansteihl A. C. 34 and 50
CIMPLICITY of design marks the develop-
" ment of the PfanstieW line of radio receivers.
The photograph and wiring diagram shown here-
with apply to both the Nos. 34 and 50 a.c. electric
receivers. The 34 is the console model, whereas
the 50 is the table model of the same receiver.
This receiving system employs 6 tubes, appor-
tioned as three stages of tuned radio-frequency am-
plification, non-regenerative detector, and two
stages of transformer-coupled audio amplification.
The wiring diagram of the system is shown here-
with. As is evident from the drawing, 226 type a.c.
tubes are used for the three radio-frequency ampli-
fiers and for the first stage of audio. A 227 type de-
tector is employed and a 171 is the output audio
tube, arranged in conventional transformer-coupled
fashion. The four 226's are wired in parallel and ob-
tain their filament potential from
a 1.5-volt winding on the power
transformer. The tuning system
used in the tuned radio-frequency
stages is conventional, consisting
of fixed inductances and variable
capacities. The method of stabili-
zation employed makes use of grid
resistances, commonly known as
grid "suppressors."
In order to attain utmost sim-
plicity, only two values of plate
voltage are applied to the receiver.
The three-radw>frequency stages
and the two audio-frequency tubes
obtain their plate voltage from the
same voltage tap, while there is
another tap for the detector. The
first radio-frequency tube's plate
voltage is governed by a potenti-
ometer type of resistance which
shunts the plate coil of the first
radio-frequency tube. The standard
grid-leak condenser system of de-
tection is employed.
The audio system is conventional
in every way. The volume control
is a voltage divider shunting the
secondary of the first audio-
frequency transformer, with the
center tap of this control connected
to the grid of the amplifying tube.
THE RECEIVER WITH ITS POWER UNIT
The secondary of the second audio-frequency trans-
former is shunted with a fixed capacity. The C bias
for the output audio tube is obtained by causing a
voltage drop across a resistance in the grid return
lead.
The receiver is divided into two parts, the radio
and audio systems being contained in one can, while
the power unit is in another can. The wiring sys-
tem employed in the power unit is standard. Two
transformers are employed. One is the power trans-
former supplying the filament and plate voltages
required for the full-wave filament type rectifying
tube, and the other is the filament transformer sup-
plying the 1.5 -, 2.5-, and 5-volt windings for the
tube filaments. The primaries of these two trans-
formers are connected in parallel and are designed
for a 115-volt a.c. line. The filament windings
supplying the 1 .5 and the 2.5. volt-
ages are equipped with voltage C9n-
trol resistances thus safeguarding
the tube filaments in the event of
an excessive line surge or increase
in line voltage. The (filter system
consists of a two-section filter, with
a single distributing resistance
across the output. The "high" side
of this resistance supplies the plate
voltage for all tubes other than the
detector tube. A tap supplies the
detector plate voltage.
The electrical balance and the
electrostatic balance in the filament
circuit is obtained by means of mid-
tapped resistances placed in parallel
with the tube systems, rather than
by tapping the filament voltage
winding.
The loud speaker coupling to
the output audio tube is direct,
without any transformer or choke-
condenser system. Two output
binding posts are provided for the
loud speaker terminals. If desired,
a loud speaker coupling unit can
be added to the receiver.
Tuning is accomplished by
means of single-dial control, the
second knob on the front panel
being for volume control.
THE PFANSTEIHL MODEL 50 A.C. RECEIVER
\T7Ant
r Gnd.
CIRCUIT OF THE PFANSTEIHL MODELS 34 AND 50. THE POWER UNIT IS SEPARATE
Building and Operating the A. C. "R. B. Lab" Receiver
By Hugh S. Knowles
HOW THE
A.C. LAB RECEIVER LOOKS— BEHIND THE PA^EL
IF THE experience of those who manufacture
both battery and a.c. operated receivers is
any criterion there is no question about the
present being an "all electric" season. This de-
mand for a.c. receivers has been reflected in the
custom set-building field where experimenters
are looking askance at any circuit which cannot
be modified to permit operation from the lighting
circuit.
The use of a.c. tubes does not alter the funda-
mental operation of a circuit and for this reason
it is quite natural to look for receivers using well-
known and tried circuits which have been modi-
fied slightly to make the use of these tubes possi-
ble.
In this connection the receiver we are about
to describe should be of particular interest to the
readers of RADIO BROADCAST. It uses the familiar
R. B. Lab circuit, with its possibilities for ex-
cellent performance with a minimum number
of tubes together with selected parts which make
possible the realization of this performance.
The circuit itself needs no introduction, since
the original and several variations have appeared
in RADIO BROADCAST. Those who are interested
in an exposition of the special features of this
circuit are referred to the June, 1926, and April,
1928, issues. The principal advantage of this over
other similar four-tube arrangements lies in its
"gain" or sensitivity and in the fact that the
balancing circuit of the Rice type gives accurate
neutralization over the whole frequency range.
The grid "suppressor" or losser method of
stabilization is not used in the radio-frequency
stage. This element of design improves the
selectivity of this circuit and makes it more
uniformly selective over the whole frequency
range.
The advantages of a.c operation have been
obtained together with an actual improvement
in performance, due to the fact that a.c. tubes
in general are somewhat better amplifiers than
the standard 201 -A type. Direct comparative
tests between this receiver and one of the battery
types indicates an improvement in gain or sensi-
tivity, better stability and negligible hum or a.c.
modulation even on the more distant stations.
One addition has been made to the circuit; a
dummy socket has been connected in parallel
with the detector socket. This makes it possible
to plug-in a phonograph pick-up permanently.
The small switch between the drum dials permits
an instantaneous change from receiver to pick-up.
This convenience will be appreciated by those
who have had to open the cabinet, remove the
detector tube, plug-in the pick-up and then
perform the inverse operation to operate the
receiver again.
An inspection of the schematic wiring diagram
in Fig. 2 will show that two minor changes have
been made in the radio-frequency circuits. The
resistance R2 has been substituted for the radio-
frequency choke previously used in the mid-tap
of the first coil, and the condenser C3 has been
added.
The resistance prevents very high frequency
oscillations which would block the first tube.
For this purpose it is just as satisfactory as the
choke and less expensive. This resistance is not
CT"HE set described here is a straight four-tube
•*• "Lab" circuit receiver, arranged to operate
entirely from the a.c. line. The results achieved are
rather better than tbose from the average four-
tube set, due to the high gain in the radio fre-
quency circuit. Mr. Knowles' receiver is a well
arranged set based on exactly the same circuit,
with the exception of provision for a.c. operation
for the filaments, that was described on page 423
in ibis magazine for April, 1928. That unusually
interesting story dealt with the engineering design
which went into this receiver and exact measure-
ments of its performance.
— THE EDITOR.
93
in any sense a "grid suppressor" at broadcast
frequencies since a high-impedance choke may
be used, or the circuit left open, for that matter.
In practice the mid-tap connection is used to
provide a means of biasing the first tube.
THE CIRCUIT
T^HE principal circuit modifications are those
* made necessary by the a.c. tubes. Three
227 type tubes are used and a lyi-A type in the
last audio-frequency stage. Heater type tubes
have been used in the radio-frequency, detector,
and first audio-frequency stages because of their
comparative freedom from hum or ripple. Tubes
of the raw a.c. type may be adjusted to give very
little hum but any change in the effective plate
voltage increases the a.c. modulation consider-
ably.
The filament current for the tubes is supplied
by a step-down transformer T8. To insure long
heater life, care should be taken to see that this
transformer is one of the new types designed to
give 2.25 volts. The old type supplies 2.5 volts.
Bias for the radio-frequency and first audio-
frequency circuits is secured by taking the drop
across a resistor in the plate circuit of the tubes.
This method is quite satisfactory where a single
stage of radio-frequency amplification is used.
No B socket-power device has been used in
the receiver since it was felt that many con-
structors would have ones which were previously
used with battery-type receivers and others
would have power amplifiers in which such a B-
power supply was included. Where this is not
the case any good quality power unit may be
used and the receiver made "all electric."
In most cases it is advisable to use a C battery
for the power tube. There is really little or no
objection to this practice since the life of the C
battery is determined by its "shelf life" which
may be in excess of a year. Details for avoiding
the use of this battery will be given later. (See
Fig. i).
94
RADIO BROADCAST
JUNE, 1928
THE LAB SET IN ITS CABINET
Special coils are available for this circuit and
receiver which require no alterations. Any of
the coils designed for a o.oooj-mfd. condenser
may be used however. The Aero 1)95 set has two
coils and will be discussed as a convenient and
typical set which may be modified.
REVAMPING STANDARD COILS
REMOVE the hinged primary winding from
the antenna coil leaving nothing but the
main secondary winding connected to terminals
I and 6. Remove the primary from the detector
coil by carefully breaking the bakelite tubing on
the inside and unsoldering the leads going to
terminals 2, 3, 4 and 5.
Tap one of the coils at the center turn verti-
cally above terminal No. I. Tap the other coil
one third of the way up from the bottom verti-
cally over terminal No. 2. Wind a thin strip of
insulating material such as thin celluloid or
varnished cambric about half an inch wide over
the center of the mid-tapped coil. Pierce a small
hole in the insulation and bring out the center-
tapped strip through it. Wind eight turns of
wire (No. 28 d.c.c. is all right, but the size is
electrically not at all important) on each side
of the midtap for the primary. Anchor the two
end turns by looping them under the vertical
bakelite coil support.
The baseboard and panel should be prepared
in the usual manner. The template drawing,
packed with the drum dials may be used as a
drilling template.
Because of the height of the drum dials, the
condensers, d and Cj, must be mounted on
"stilts" or bushings. In this case two pieces of
brass tubing cut to the proper length were used.
As the condensers are mounted in this receiver,
the reading of the drums increases with wave-
length. If the readings are to increase with fre-
quency the condensers should be reversed. The
full floating shafts make this possible. This
feature also permits bakelite or hardwood shafts
to be substituted. These will be discussed under
the operating details.
The location of the parts is very important.
In experimenting with the layout, for example,
it was found that moving the choke, (L<), over
between the drum dials made the set unstable.
This trouble was found to be due to the greater
length of the "hot" plate lead and not to cou-
pling between the choke and coil as might have
been supposed. A discussion of the important
leads to watch appeared in the June, 1926, RADIO
BROADCAST under the title "Additional Notes on
the R. B. Lab Circuit."
There is nothing "tricky" about the wiring.
All a.c. filament leads should be twisted. Bus
bar wiring was used in this set so the connections
could be easily traced in the photographs. All
the battery leads may be cabled if flexible wire
is used. There is no objection to using "bee"
line or direct point to point wiring if the leads
are carefully spaced. For details on the arrange-
ment of the leads see the photographs and
Fig- 3-
The two A-battery leads on the cable are not
used. If an outside C battery is to be used for
the radio-frequency and first audio-frequency
stages it may be added by making the following
changes: Remove Rs and Cj and connect the
leads going to the K terminals on the 227 sockets
to the minus B or yellow cable terminal. Connect
the lead going to the minus C terminal of the
first audio-frequency transformer and the one
connected to R% to the black cable terminal.
Connect C? across the black and yellow cable
terminals. The C battery is then connected
externally by using the yellow and black
leads as the positive and negative leads re-
spectively.
WHEN A B-POWER UNIT IS USED
I F B-power unit which supplies 180 volts is
' used, a C battery with proper potential for
the tube employed should be used for the power
tube. Where the power device supplies 200 volts
or more, an arrangement such as indicated in Fig.
I may be used. A jo-henry choke and 2.0- or 4.0-
mfd. condenser should be used to keep the direct
current out of the speaker. When the speaker
return is connected as shown, the 2ooo-ohm grid
biasing resistor is not in the return circuit and
this insures better reproduction of the lower
audio frequencies.
No output device is used in the receiver. This
reduces the cost of the parts when a I12-A type
tube is used or a lyi-A type with only 135 volts
on the plate. If an external power amplifier is to
r|G<ay
Q |
B- Del Int.
B SocXet-Powei
Unit
Power
AN UNUSUALLY EFFICIENT SET IN SMALL SPACE
FIG. I
be used the last audio-frequency transformer may
be omitted. In some cases the power amplifier
includes an audio stage ahead of the power tube
and in this case the detector output may be con-
nected directly to the speaker jacks on the cable
terminal.
The dial lights should be connected in parallel
across the filament of the lyi-A tube.
Very little adjustment should be necessary
after the receiver is completed. In adjusting the
balancing circuit the "dead filament" method is
not very desirable nor convenient in this case.
Tune-in a carrier in the short-wave section of
the broadcast band and set the detector regenera-
tion control so the set just oscillates. Use a screw
driver made from a bakelite or fiber strip to ad-
just the balancing condenser. Tune the radio-
frequency stage first to one side of the carrier and
then to the other slowly while adjusting the
"equalizer."
JUNE, 1928 BUILDING AND OPERATING THE A. C. "R. B. LAB" RECEIVER
95
constructor prefers to make his own coils, are in-
dicated on the diagram, Fig. 2.
PARTS LIST
Li, L, Aero Products Co., (i) Pr. U-95,
or Special Lab. Coils . ...
Ci, Cj Hammarlund, (2) ML-2J Con-
densers . .
G Hammarlund, (O-MC-ij Midget .
U Hammarlund (i) RFC-S; Choke .
C* Hammarlund, (i) Equalizer
Micarta (Westinghouse Co.), (i) 7" x
21" x|" Black Panel . . .
Ri Electrad (i) Type P Volume Control
R2, R3 Electrad (2) joo-Ohm Grid Type
Resistors
Re Electrad, (i) V-jo Resistance . .
R< Electrad, (i) V-io Resistance .
Yaxley, (i) 669 Cable
Yaxley, (i) S.P.D.T. Switch No. 30 .
Ti, T2 Silver-Marshall, (2) 240 Audio
Transformers
T3 Silver-Marshall, (i) 247 Filament
Transformer
y, (3) 5-Prong Sockets
y, (2) 4-Prong Sockets
FIG. 2
Eby,
Eby, (2) Binding Posts
C;, Cs Tobe, (2) i.o-mfd. Bypass con-
densers .........
C» Aerovox, (i) 0.00025 Grid Conden-
ser ..........
R8 International Resistance Co. (i) 2.0
Meg. Grid Leak ......
International Resistance Co., (i) Leak
Mount .........
National Co., (2) Single Drum Dials .
$ 8.00
1 1 .00
2.OO
2.OO
5°
2.20
1.50
50
•75
•75
3-25
90
12.00
5.00
1.50
.80
30
i. 80
.40
.50
.50
9.00
When the adjustment is properly made there
will be a slight "swishing" sound as the r.f.
circuit is tuned to the station and the signal will
clear up. If the detector is placed on the point
of oscillation, there will be no tendency for the
r.f. stage to make it oscillate as the r.f. dial is
turned. It may be necessary to readjust the
regeneration control, (Cs), slightly to make the
balance adjustment more exact although the
setting is not very critical.
After the set is balanced, the effect of hand-
capacity should be tried on a weak station. If
there is any appreciable effect, a bakelite or
hardwood shaft should be substituted for the
brass one used with each condenser. The effect
may be further reduced after this change has
been made by grounding the metal frame of the
dials.
If the antenna stage tunes broadly it is an
indication that the antenna is too large and the
effective capacity should be reduced by connect-
ing a fixed condenser about o.oooi-mfd. capacity
in series with the antenna lead. The selectivity
of the first stage should be measured with the
volume control in the full "on" position since
this resistance reduces the selectivity. When the
set is tuned to a station where the volume control
is near the "off" position, the question of selec-
tivity is never important.
Since the volume control is in the radio-
frequency circuit, special provision must be
made for controlling the volume of the phono-
graph pick-up arrangement. Nearly all of the
standard pick-ups with which we are familiar are
sold with a special volume control.
To minimize hum, the B-power circuit should
be grounded. Usually the ground works most
satisfactorily on the minus B lead. In some cases
the hum is reduced by grounding the plus 45-volt
tap which in this set connects to the neater
winding mid-tap. Only one of these leads should
be grounded, however.
If an outdoor antenna is not available, the
experimenter may try connecting a o.oo2-mfd.
fixed high quality mica condenser from one side
of the house-lighting circuit to the antenna
binding post. Both sides of the line should be
tried since one side may be grounded. In this
case the line acts as the collector and the signal
is brought to the receiver much as it is in carrier-
current telephony.
The list of parts below are those used in the
model described here. Other parts, electrically
and mechanically similar, may of course, be
used.
The coils Lj and Ls are special and are sup-
plied by Aero Products. If the builder desires to
revamp the standard Aero coil set, No. Ugs, he
should follow instructions on page 94. The
dimensions for all the coils, in the event the
865.15
ADDITIONAL PARTS
(Needed to complete the set as described),
(i) Phonograph pick-up, with volume control.
(i) B Power-Unit, furnishing a maximum voltage
of 220, at 40 mils., with taps as follows: 45,
90, 180, -40.
(3) a. c. 227 type tubes.
(i) Power tube, Type 1 12-A or I7I-A (See Text).
(i) C Battery (Optional, see text; rating depends
on power tube used),
(i) Corbett cabinet to accommodate panel
(7x21 x|").
FIG. 3
Using the Screen-Grid Tube in Popular Circuits
By THE LABORATORY STAFF
M'
"ANY experimenters have written the
laboratory for information to enable
them to use a screen-grid tube in the
r.f. stage of such circuits as the R. B. Lab.,
Universal, Aristocrat, Browning-Drake, and
other sets consisting essentially of a stage of
radio-frequency amplification followed by a
regeneratve detector. The adaptation of this
tube to the latter receiver has been described in
the May RADIO BROADCAST and, in the same is-
sue was described an a.c.-operated all-wave
receiver using a screen-grid r.f. stage with the
tube operated with a.c. on its filament.
There were no special problems involved in
the design of an a.c. Lab set using a type 227
tube in the r.f. stage and the construction of
such a receiver was completed with little trouble;
the result of this work has been described in the
preliminary article in the April issue and in the
construction article appearing in this issue.
After the construction of the a.c. set had been
completed, experiments were made to deter-
mine how satisfactorily the type 222 could be
substituted for the 227 in the r.f. stage.
The tests described here have been confined
to the "Lab" receiver, and since individual
tests on the various receivers mentioned in the
first paragraph have not been made it cannot
be stated positively that the tube will work
equally well in all these circuits. However, since
they are all essentially the same, the operation of
the screen-grid tube as an r.f. amplifier, in these
various sets, shouldn't differ very much.
The experiments on the "Lab" circuit were
begun by first setting up the receiver for opera-
tion with a 227 in the r.f. stage. A modulated
oscillator (the construction of which was de-
scribed in the June, 1927, issue) was located about
10 feet away and its output cut down until the
signal from it was just audible in the output of
the "Lab" set. The 227 was then removed and
the circuit rewired for the screen-grid tube in
place of the type 227 tube in the r.f. stage with
the filament of the screen-grid tube operated
from a storage battery. The circuit is given in
Fig. I. The plate of the screen grid is coupled,
through a fixed condenser, C, with a value of
o.oooi mfd. or larger, to the grid end of the coil
in the detector grid circuit. The plate voltage
for the cx-322 is obtained through the r.f.
choke. Using the 322 there was quite a defi-
nite increase in the output of the "Lab" re-
ceiver. The change in detector plate current —
which is a measure of the signal impressed on the
grid of the detector — was too small to measure
when the 227 was used. With the screen-grid
tube, the change in plate current was quite no-
ticeable indicating a definite increase in gain
due to the screen-grid tube. This circuit has the
disadvantage that the 322 must be supplied with
filament current from a battery source. The fila-
ment of a 322, being the same as that in a 120
type tube, requires 0.132 amperes at 3.3 volts
which may be supplied economically from three
dry-cells but it would, of course, be an advantage
if the filament could be operated by a.c. supplied
by the filament transformer used to heat the
filaments of the tubes in the circuit.
The next step, therefore, was to rewire the
"Lab" circuit for a.c. operation of the cx-322
using the same circuit as was used in the all-
wave receiver. The plate voltage was 135 volts
and the screen voltage 45 volts, both obtained
from B batteries. Filament voltage is obtained
by connecting the 1.5- and 2.5-voIt windings on
the filament transformer in series as indicated in
the circuit, Fig. 2, so that the voltages add.
The voltage is then reduced to 3.3 by means of
a 5-ohm resistance connected in series with one
side of the filament circuit. If the two windings
are connected so that the voltages buck each
other the filament of the screen-grid tube will
not light and the connections to one of the wind-
FIG. 2
ings should then be reversed. A i5OO-ohm re-
sistor, by-passed with a o.oi-mfd. (or larger)
fixed condenser, is connected between the center-
tapped resistance and minus B to supply C volt-
age for the grid of the 322 type tube. The com-
plete circuit is given in Fig. 2.
This complete a.c. circuit for some reason,
not yet determined, seems much more tricky
than the d.c. circuit of Fig. i, and in general,
the performance of the circuit with a.c. on the
322 filament was not altogether satisfactory.
The operation of this complete a.c. model had
the disadvantage that the output of the receiver
contained a loud hum when the detector was
put into oscillation and the two tuning circuits
brought into resonance. Apparently under such
conditions the 322 began to oscillate. A definite
increase occurred in the current flowing in the
screen grid circuit. This trouble was not caused
by common coupling in the battery supplying
the screen circuit for the same effect was no-
ticed with a separate battery supply to the screen
grid.
When the detector circuit was not oscillating
the output of the receiver was quiet. Therefore,
the only practical disadvantage of the arrange-
ment was that it made it difficult to tune-in
signals, especially weak ones, by means of a
squeal for the hum is loud enough to make
a faint heterodyne whistle inaudible.
Some experiments were now made using a
neutralized circuit. In this model of the "Lab"
receiver, the lead from the plate of the r.f. am-
plifier to the detector coil is several inches long
and, although when using a 227 in a Rice-
neutralized amplifier the long lead will have no
effect on the stability of the circuit, it was
thought that it might be causing some trouble
when using a 322 without neutralization. We
therefore changed the circuit of the r.f. stage to
that given in Fig. 3. The small twisted lead con-
Q.6
nected to the grid and plate of the 322, consisted
of two 2-inch lengths of insulated wire twisted
together. These wires constituted a small con-
denser and were used to increase the grid-plate
capacity of the tube to about o.ooooi mfd.
(10 mmfd.) so that the circuit might be neutral-
ized with a standard neutralizing condenser.
The neutralized receiver gave somewhat more
stable operation than the unneutralized circuit
but the hum, with the detector oscillating, was
still present.
As a result of these experiments we are un-
able, for the present, to recommend the use of
a 322 in the "Lab" circuit with its filament oper-
ated on a.c. Those of our readers who have a
d.c. operated "Lab" receiver may use a 322 in
accordance with the circuit given in Fig. i
and the receiver will give somewhat greater
gain than was obtained using a 2Oi-type tube.
In some cases it may be found that the selec-
tivity of the circuit using a screen-grid tube is
not as good as when using a 2OI-A type tube as
the r.f. amplifier. The selectivity may be im-
proved, however, by substituting a midget vari-
able condenser with a maximum capacity of
o.oooi mfd. for the fixed o.oooi-mfd. condenser
connected between the plate of the screen-grid
tube and the grid end of the detector coil. The
selectivity of the circuit may be adjusted to a
satisfactory value by varying the setting of this
small condenser.
The results of these experiments will be ap-
plicable to other receivers of the same type as
the "Lab" set. To revise these other receivers
for screen-grid operation, it is simply necessary
to remove the connection to the NP winding,
i.e., the primary and neutralizing windings of the
r.f. transformer and then connect a lead from
the plate of the 322 through a condenser with a
capacity of about o.oooi mfd. or larger to the
grid end of the secondary coil in the detector's
grid circuit. Voltage for the plate of the screen
grid tube should be supplied through an r.f.
choke, Fig. i, which should have an inductance
of 85 millihenries or more.
Experiments, as have been described here, can
readily be duplicated in a home laboratory.
To many of our readers, experimenting with
sets and circuits in their own small iab., equipped
in many cases with instruments made from de-
scriptions that have been given in RADIO
BROADCAST, is proving an intensely interesting
part of their radio training. How much one really
knows quantitatively about radio engineering,
depends almost directly upon how many and
how systematically experiments have been
made; experiments not carried out with a definite
aim in view, generally yield no concrete results
and do not greatly increase one's knowledge of
radio phenomena. The Laboratory will always
be glad to hear from any readers who do, or
have done, any such experimenting.
AA[ EAST SET TO BUILD
Little explaining need be done if this illustration is compared with Figs. I and 2. The "loop tap" indicated by
the f end! is not used in this set but is shown merely to indicate how this type of lap is made. In this coil, the
tap employed is near the detector and cannot be seen in this photograph.
THE receiver illustrated above is sim-
ple to built, costs but little, delivers
high-quality signals, and is reasonably
selective. It provides an excellent receiver for the
beginner to try his hand at — after having put
together this array of apparatus he has the whole
world of radio home construction at his feet.
There are many people who would like to listen
to local broadcasting without a great expenditure
of cash, either for the radio set or for its upkeep.
This set will provide good signals from broad-
casting stations not too far away at small cost.
The receiver consists of a tuner, a crystal de-
tector, an amplifier and a pair of head phones.
Anyone with a soldering iron and a pair of pliers
can assemble it in an hour. The disadvantages of
the receiver are few: it is not selective enough to
distinguish between stations operating within
30 kc. of each other; it will not receive the
"coast"; but for reception from locals or power-
ful stations up to 100 miles away it is excellent.
Because of the special electrical characteristics
of the crystal — in this case, a piece of carborun-
dum— it is possible to use a high-ratio audio-
frequency amplifying transformer. The step-up
as between primary and secondary circuits in
this case is 6:1. Any present-day transformer of
such high ratio, used with a vacuum tube detec-
tor circuit would give comparatively poor quality
— the low notes especially would suffer.
The coil can be made at home, or any com-
mercial coil may be employed provided it has
the proper number of turns to cover the broad-
casting band with the condenser used and pro-
vided it is not too difficult to solder a few taps on
it. The condenser may be any assembly that
happens to be in the builder's junk box. Natu-
rally, the better the coil and the condenser the
better the final result.
A good way to wind the coil is to place a
rat tail file, a pencil or a piece of dowel rod
through the spool containing the wire which is
to be wound on the coil form and to place the
By KEITH HENNEY
Director of the Laboratory
spool on the floor. Two holes are drilled in the
ends of the coil form and one end of the wire from
the spoil is looped through one of these holes. A
weight, one's feet for example, is placed on the
rat tail file, and the wire wound on the form.
The purpose of the weight is to keep the wire
taut so that it goes on the form tight enough that
it will not fall apart under temperature or humid-
ity changes. When the proper number of turns
has been wound, the wire is cut and the end
looped through the second hole in the coil form.
The diagram, Fig. i, indicates the exact number
of turns recommended for this receiver. Taps
should be made at three places, dividing
the coil into four equal parts. These can be
made by twisting a loop of wire when it is wound
on the form or by soldering short lengths of wire
to places where the insulation has been scraped
from the wire after winding. The loop method is
shown in the photograph above.
Strongest signals will be obtained with the
antenna wire attached to one end of the coil and
the ground to the other. At the same time the
selectivity will be poorest. To improve the selec-
tivity, the antenna may be tapped on to the coil
as shown in the accompanying illustiation, or an
additional winding of about 10-20 turns may be
wound about the larger coil and the antenna and
ground attached to it. The antenna should be
about 75 feet long.
Still greater selectivity may be obtained by
tapping the detector circuit to only a part of
the coil. Note that this was done in this receiver.
See Fig. I. This is because the crystal is a low
impedance detector and increases the effective
resistance of the tuned circuit consisting of the
coil and condenser. When tapped across part
of the coil this increase in resistance, and result-
ing decrease in selectivity, is not so marked.
The arrangement used in the Laboratory is
shown in Fig. 2. In the Laboratory, signals
freer from outside noise or "interference" were
secured by not grounding the crystal circuit.
97
This may not be the case generally and for this
reason the constructor should try grounding the
circuit as shown in the dotted lines.
With this receiver, tested in our Laboratory,
and using the tapped arrangement, it is possible
to hear wjz 30 miles away when WEAF is operat-
ing 8 miles away although with bad interference.
With a wave-trap tuned to WEAF, considerable
improvement in wjz's signals is noted, wjz can-
not be heard at all if the detector is connected
across the entire coil.
The parts actually used in the set photo-
graphed follow, and any similar apparatus may
be used. It is even possible to hear signals with
a crystal, home assembled, such as galena or
silicon — a very cheap detector. The home
constructor is advised against such procedure.
The Carborundum unit is recommended because
it is a compact, stable, and sensitive unit, and
because it is possible to use a biasing voltage on
it to increase its sensitivity.
The constructor may use a small flash-light
cell as the biasing battery or he may use the
voltage obtained from dry cells used to light the
filament of the amplifier tube. Using the extra
cell is simpler, but has the disadvantage that it
is an additional unit which needs replacement.
If the dry cells are used, the dotted lines in the
diagrams should be followed, or as in the insert
in Fig. 2, where the voltage drop across the
rheostat is used.
It does not matter where the various parts are
located on the base board. One arrangement is
shown in the photograph. The picture wiring
diagram, Fig. i, shows where the wires go.
The signals from this receiver may be amplified
by any of the power amplifier units now readily
obtainable. If a two-stage amplifier is used,
such as is made by Samson, Amertran, Silver-
Marshall or others, the output of the detector
may be used and the amplifier tube, transformer,
and accessory apparatus shown in this model may
be eliminated. (Dotted lines in Fig. 2)
RADIO BROADCAST
JUNE, 1928!
The rheostat is used to turn on and off and
to control the current through the amplifier fila-
ment. It should never be turned on further than
is necessary to bring in the signals at proper
volume. An experiment will show that turning it
beyond this point does not increase signal
strength. As a matter of fact such a procedure
only decreases the life of the batteries and the
tube. One 45-volt B-battery block and three dry
cells will last several months with such a simple
receiver.
After constructing such a receiver there is the
possibility of adding another stage of audio
amplification for loud speaker signals, and the
Laboratory will be pleased to supply information
on how to do this to those who write. There is
also the possibility of adding a stage of radio-
frequency amplification to such a receiver,
FIG.
How to place and connect the parts employed
Omit if used with Power
Amplifier having_twp_ stages "_^
v-To one dry cell
FIG. 2
Circuit diagram of the crystal set and one stage of audio amplification. The insert
shows how the detector bias may be obtained from the voltage drop in the rheostat
SIMPLICITY ITSELF
The panel is 7" X 12" and can be fitted into any cabinet which suits the owner. The
Remler dial noted in the parts list was not available when this photograph was taken
thereby making it much more selective and sensi-
tive and as a result to increase its distance-
getting ability. In fact, a three-tube set using
the Carborundum unit as a detector provides
the listener with a high quality, reasonably selec-
tive receiver for reception from stations within
• several hundred miles. The Laboratory has re-
ceived a number of letters from readers who have
done very creditable DX work on such an outfit.
How such a receiver as is described here is
used in RADIO BROADCAST Laboratory may be of
interest. At times considerable noise is picked
up in the Laboratory from the presses, which
print RADIO BROADCAST and many other maga-
zines, making the testing of receiving equipment
impossible. Down at the shack, a distance of
about looo feet from the Laboratory where 2 or
is located the "air" is quiet. The receiver illus-
trated here is installed there and permanently
tuned to WEAF. The output from the detector is
sufficiently high that it can be placed on a wire
line coming to the Laboratory where it is fed
into a two-stage amplifier and thence to a loud
speaker. When necessary, the first-stage amplifier
on the base board with the detector is thrown
into the circuit by means of an extra line and
the output from it is put on a third pair of wires.
This output may be used in connection with a
single power stage or loud speaker operation. At
all times, when near-by broadcasting stations
are on the air we have good signals available in
the Laboratory for testing purposes.
THE LIST OF PARTS
The experimenter who already has odds and
ends of radio apparatus in his possession can
probably assemble the receiver described here
without the purchase of much additional appara-
tus. The parts listed below were used in the re-
ceiver described, although of course any others,
electrically and mechanically similar may be
selected.
Ci — Remler 0.0005 mW- type No. 639 conden-
ser Remler standard dial
L2 — 52 turns No. 24 s.c.c. copper wire
wound on 3" form
LI — 10-20 turns No. 28 a.s.c. copper
wire
Ti — General Radio No. 285 audio
transformer
Ri — Frost 3o-ohm rheostat
Carborundum Company detector
unit
Frost UX type socket
Fahenstock spring clips (8)
One — ux-igg vacuum tube
One — Westinghouse Micarta panel
One — Wood baseboard
3— dry cells
One — set Trimm headphones
Phones or
Power
Amplifier
I Three dry
cells
T1
LOUD
SPEAKER
JACK
POWER TUBE
SOCKET
OUTPUT
TRANSFORMER
T4
POWER LEAD
fo 110 VOLTS
60 CYCLE A.C.
110 VOLT
LINE SWITCH
FILAMENT
TRANSFORMED. T3
THE EVER-POPULAR ROBERTS SET WITH A. C. OPERATION
The illustration is lettered to agree with the list of [tarts on page 101 and with Fig. 3. The circuit diagram. This
model of the a.c. Roberts reflex circuit was built to fit in a phonograph cabinet. It is unnecessary for the con-
structor to follow this layout for wide latitude is allowed by this circuit in this respect
A Three-Tube A* C,
By ELMER G. HERY
F THE thousands of set-builders who
have constructed the original three-tube
Roberts, few have been won over to
any other circuit unless they have gone to a
much more elaborate and expensive layout. For
those who know the merits of the Roberts cir-
cuit, a.c. operation as described in this article
is almost inevitable.
Beginners will find in this receiver a set which
is easy to construct and uniformly excellent in
results as to the quality, selectivity, sensitivity,
volume, and distance reception.
An important feature is that this circuit does
not require the most expensive pieces of equip-
ment. It may be constructed from whatever ma-
terials are at hand. The skeptical may make a
rough assembly of old parts, and then convince
himself that the substitution of any good low-
loss parts will give better results. [The list of
parts and the photographs show exactly what
was used in the set described by the writer. The
parts are all standard and readily available.
Wide substitution can be made, according to the
desire of the constructor. — Editor.]
Another good feature is the fact that the ar-
rangement of parts and the panel shape do not
affect the results. This circuit has been built by
the writer on square panels and on long narrow
panels, and to fit in all kinds of cabinets with
excellent reception in all cases.
The first thing to consider is the coils. Manu-
factured coils may be used if desired. The writer
has used Sickles and Hammarlund-Roberts with
perfect satisfaction. If the set-builder desires to
make up his own coils they can easily be made.
Thirteen-point spider-web fiber forms are re-
quired. They may be obtained from the lo-cent
stores. The antenna coil consists of thirty-five
turns wound over-two-and-under-two spokes,
with a twisted loop or tap every five turns.
There are two secondary coils Li and Lt, and each
consisting of forty-four turns wound over-two-
and-under-two spokes. The tickler coil, LS con-
sists of twelve turns wound over-two-and-under-
two spokes. These four coils are all made of No.
The A. C. Roberts Receiver
THE Roberts receiver, first introduced by
RADIO BROADCAST in 1924 won many friends
for radio and many for ibis magazine. It has been
constructed by more than 100,000 radio fans and,
in one form or another, is still giving satisfactory
service all over the world. The circuit is so effi-
cient— considering the number of tubes employed
— and so easy to build and operate that its popu-
larity, like a certain famous cigarette, is deserved.
Many readers are still interested in building the
circuit and Mr. Hery's article here gives them full
instructions and a wide latitude in construction.
For those who are interested in making over their
present Roberts set for a.c. operation, the last part
of this article provides sufficient information. The
circuit shown here employs the original reflex ar-
rangement. Those who desire to employ a straight
audio stage and eliminate the reflex may secure
information by writing to our Technical Informa-
tion Service.
— THE EDITOR.
99
22 double cotton covered wire. The NP coil Li,
is made of No. 26 double cotton covered wire.
This coil consists of a double winding; that is,
two parallel wires wound over-one-and-under-
one spoke, with eighteen turns. In other words,
there are two concentric coils of eighteen turns
each. The wire may be twisted or kept flat,
preferably the latter.
The antenna coil and its secondary coil are
mounted on the same shaft about j" apart. A
long brass machine screw ($\" or more) makes
an ideal mounting arrangement, using a nut on
either side of each coil to hold it rigid. The ma-
chine screw is bent to give any desired mount-
ing angle to the coils, and fastened through
the baseboard with a nut. (See Fig. i) Fig. i-B
also provides a very simple mounting through
one of the spokes of one coil.
A standard mounting for the tickler coil is
an arm with knob for panel mounting. The NP
and secondary coils may then be mounted on a
screw through the baseboard as shown in Fig. 2.
The dotted lines show the tickler coil in the
raised position.
It is important that the antenna coil and its
secondary be mounted so that the direction of
rotation of the windings is the same for both
coils. Likewise the NP, Secondary, and Tickler
coils should be wound in the same direction.
One way to avoid trouble from this source
is to proceed as follows: when the coils are
wound, mark on the forms an arrow which points
around the form in a clockwise direction. Then,
starting from the inside and proceeding to the
outside of the form, the wire should be wound
100
RADIO BROADCAST
JUNE, 1928
FIG. IA-B
Details for mounting and tapping the coils
on in a clockwise direction. The coils in each
assembly should be arranged so that all of the
arrow marked sides face in the same direction.
The two groups of coils should be mounted as
far apart as mechanically possible, and at right
angles to each other.
After the coils have been mounted and the
positions of the other pieces of equipment have
been determined, the inside and outside leads of
each coil may be brought to the most convenient
spoke of the spider-web form, and fastened
through a hole in the spoke by means of a screw
and nut (see diagrams). Then the spokes may
be cut off to within f" of the wire on the coil,
thus reducing the over-all size of the coils.
For connections, the outside and inside leads
of coils are indicated on the wiring diagram by
"O" and "I" respectively. The center point of
the NP is coil indicated by "M." The coils as
they appear on the wiring diagram, Fig 3, from
left to right are as follows: Antenna, LI, antenna
secondary, Lj, NP, La, and Ln, secondary, L4, and
above the secondary, the tickler coil, Lj.
The taps on the antenna coil may be connected
to an inductance switch if desired, but a simpler
method is to place a test clip (See Fig. I A) on the
end of the ground lead, and clip to the tap which
gives the best results. The longer the antenna
in use, the fewer turns will be required on the
antenna coil. One tap will be found which will
give satisfactory results on all wavelengths.
The method of obtaining the mid-point "M"
of the NP coil may require some explanation.
"M" is obtained by connecting the inside end
of one winding with the outside end of the other
winding. Two different colors of wire may be
used to avoid confusing the two windings, or a
flashlight bulb may be lighted through each
winding to locate the corresponding inside and
outside ends.
LOCATING THE APPARATUS
THERE is nothing special to be said about the
locating or mounting of the remaining equip-
ment, with the exception, of course, that the grid
and plate leads should be kept short. The photo-
graphs give an idea of a good baseboard layout
which was designed to fit a phonograph cabinet
and to include all the a.c. power supply appara-
tus. The panel layout suggested may easily be
modified to suit the size and shape of the panel
used by the constructor who duplicates this re-
ceiver.
The switch mounted on the panel controls
the line current supply and should be of a size
and capacity equal to wall switches used for
house lighting. A simple method is to use the
body of any ordinary no-volt tumbler switch
and mount it directly on the panel with a slot
cut in the panel for the lever.
No rheostats are needed when the a.c. tubes
are used, and the volume control may be a
25,ooo-ohm potentiometer in the antenna circuit
or the volume control may be as indicated in the
model described here, i.e., a variable resistance
such as a Clarostat or Bradleyohm across the
secondary of the first audio transformer. No
loud speaker jack is shown on the panel, as
modern practice tends toward mounting this
at the back of the set if it is used at all, with
the antenna and ground binding posts.
As to the make of tubes to be used, there is
little choice between standard, reliable prod-
ucts. There has been considerable doubt on the
part of prospective set-builders as to whether the
a.c. tubes will give very long usage. For those
who prefer to make certain, a written guarantee
is given with some makes to replace tubes free
of charge if they fail to function for one year.
This should satisfy the demands of the most ex-
acting buyer. This article describes the use of
a.c. tubes which employ the Radiotron type
bases, although the set will work excellently
with the Sovereign or Kellogg a.c. tubes. In the
event that the builder uses this type of tube,
the major difference between that construction
and this is in the a.c. filament circuit.
No rules need be observed in the assembling
of the set, except that the filament leads should
be isolated as far as possible from all other
leads, and especially from grid leads. The pho-
FIG. 3
Diagram of connections. Those who desire to convert their d. c. Roberts sets
can follow this diagram and instructions on this page and the one following
'•.- Base Board
FIG. 2
The coils and their relation to the panel
tographs show how this may be accomplished.
It is undoubtedly wise to complete all other
wiring of the set before starting the filament
wiring, to avoid any possibility of connecting
filament leads to any other part of the circuit.
The filament current may be obtained from
a filament transformer. If a 1 12 or 171 type tube
is to be used for the last amplifier, the filament
transformer should have three voltages; namely,
i^ volts, 2j volts, and 5 volts. Some B power
units provide a 5-volt winding which may be
used for the amplifier tube, in which case only
the two lower voltages need be supplied by the
filament transformer. If a 210 type tube is used
for an amplifier yj volts are required for the
filament, and this voltage is usually provided in
the power pack or powerizer being used for plate
current.
Any good filament transformer may be used,
some makes furnishing mid-taps for the 2|-volt
and 5-volt windings. It is not wise to use a mid-
tap in the transformer on so low a voltage as
I j, so that instead a mid-tap resistance or a po-
tentiometer, Re, is used to obtain the mid-point
of the ij-volt winding. The mid points of the
2j-volt and 5-volt windings may be obtained
in the same manner if the transformer is not
provided with mid-taps.
SECURING GRID BIAS
FOR grid bias on the reflexed tube, the center
point of the mid-tap resistance is connected
to one side of a looo-ohm resistor, Ri, The other
side of the resistor is connected to ground and
there is a i.o-mfd. condenser, C;, across the re-
sistor. For grid bias of the power tube, the mid-
tap of the filament transformer winding supply-
ing this tube is connected to a resistance of
2000 ohms, Rs, the other side of which is con-
nected to ground. A i.o-mfd. condenser Cs is
placed across this resistance. This value of re-
sistance is satisfactory for 112 and 171 type
tubes.
Some tube manufacturers recommend a posi-
tive grid bias for the heater of the detector tube,
and some recommend negative bias. In this cir-
cuit no bias has been found necessary. The mid-
tap lead of the 2^-volt winding may be con-
nected to plus 45 instead of to ground in the event
that there is excessive hum in the output of the
receiver.
A 227 type tube may be used in the reflex
position if desired, but satisfactory results should
be obtained with the 226 type, and this type
is somewhat cheaper than the 227 type.
Each pair of filament leads must be twisted
with about two or three twists to the inch to
avoid hum. Likewise, the leads which go to the
tumbler switch on the panel should be twisted,
as well as any other a.c. leads in or around the
set. For filament wiring, no smaller wire than
No. 14 should be used, as the a.c. tubes draw a
much heavier current than the d.c. tubes. For
JUNE, 1928
A THREE-TUBE A. C. OPERATED ROBERTS RECEIVER
101
wiring the balance of the set Celatsite
or similar hook-up wire is recom-
mended.
CONVERTING YOUR D. C. ROBERTS
FOR the conversion of a storage-
battery-operated Roberts set to
complete a.c. operation, the 'wiring
diagram and the instructions already
given are perhaps sufficient. The sub-
stitution of a B- power unit for a B
battery needs no explanation. Ob-
taining grid bias without C bat-
teries, though sometimes confusing,
should be clear from the diagram.
A C-battery in the grid circuit
puts the grid voltage below the filament
voltage, whereas a resistance between the
filament circuit and ground places the filament
voltage above the grid voltage. The effect
is the same in either case. The C batteries
may first be removed and connections made in
their place as shown in the diagram. Next, the
filament leads of each tube in the d.c.-operated
set may be increased in size if necessary to carry
the heavier current taken by a.c. tubes. [Wire
tables showing current carrying capacity will
give this information. Or see RADIO BROADCAST
Laboratory Information Sheet No. 141, Nov-
ember, 1927, issue. — Editor.) Care must be taken
in this changeover to a.c. not to remove any leads
which serve some purpose other than lighting the
d.c. filaments. A "UY" socket may now be sub-
stituted for the ux socket in the detector posi-
tion, and the same grid and plate leads that
were connected to the ux socket go to the UY
socket. If an output transformer or filter is not
in use, one should be installed as shown.
In the list of parts given here, some names of
equipment are mentioned because of successful
experience with these makes. Perhaps other
makes will give equally good or even better
results, but some experimenters often like to have
something definite in mind when they do their
purchasing. In the case of the variable conden-
THE ALL IMPORTANT CONTROLS ARE HERE
sers, a rugged low-loss construction such as
General Radio is strongly recommended. The
parts required for conversion of the d.c. set to
a.c. are indicated separately at the end of the list.
The values given for fixed condensers, resis-
tances, etc., will generally be found satisfactory,
but they may be experimented with after the
set is in operation, for possible improvement
to suit the taste of the user.
LIST OF PARTS USED
Ci, Cj — General Radio o.ooo5-mfd. variable
condensers.
C3 — Hammarlund g-plate neutralizing con-
denser.
Ct — Dubilier o.ooo25-mfd. fixed condenser
with clips.
Q — Dubilier o.oooj-mfd. bypass condensers.
Ce — Dubilier o.oo25-mfd. bypass condenser.
C?, Cs — Aerovox i.o-mfd. bypass conden-
sers.
RI — Clarostat volume control resistor.
R2 — Tobe Tipon grid leak (about 2.o-meg. al-
although various values should be tried).
Rs — Hardwick-Field C-bias resistor, 2900-
ohms.
Ri — Ward-Leonard C-bias resistor, 1000
ohms.
Ri, — General Radio center-tapped resistor.
Ti — Amertran AF-6, 5:1 audio transformer.
T2 — Thordarson R-2OO audio trans-
former.
T» — Acme Apparatus AC-2 filament
transformer.
T4 — Bremer-Tully output device.
—Frost open-circuit jack.
— General Electric tumbler switch.
5 — Spiderweb coil forms and 2 coil
mounting arms.
— Wire for coils: j-lb. No. 22 d.c. c.;
J-lb. No. 26 d.c.c.
2 — Benjamin ux sockets.
I — Benjamin UY socket.
2 — Marco dials.
5 — Eby binding posts.
— No. 14 lamp cord for a.c. circuit.
— 25 ft. Celatsite hook-up wire.
Test clips, screws, nuts, baseboard,
and Westinghouse Micarta panel.
ADDITIONAL PARTS
i — B-power unit supplying the following
voltages: 45, 90, 135, 180
i — Type 227 a.c. tube
I — Type 226 a.c. tube,
i — Semi-power tube, either 112 or 171 type
The coils used in the set described are
home-constructed according to directions
in the article. Sickles or Hammarlund-
Roberts coils may be used if the builder
prefers to use manufactured coils.
The circuit and building instructions deal
with the 226 and 227 type of a.c. tube
although as indicated in the article, the
Sovereign or Kellogg heater type a.c. tubes
can be employed equally well if the con-
structor makes the necessary filament
circuit and mechanical changes required.
If one has on hand a d.c.-operated Roberts
receiver which is to be changed over to a.c. .
operation, it will of course be possible to use in
the revised set most of the parts contained in
the d.c. model. Only the following items in the
above list of parts need be purchased, in chang-
ing a set from d.c. to a.c. operation: Cy, C«, Rs, RI
Re, T3, one Y type socket and a line switch.
THE BASEBOARD ALLOWS ROOM FOR A B-POWER UNIT
This provides complete a.c. operation with maximum simplicity
hhX II
KY
The Simplest Receiver
N A recent visit to KDKA I had demon-
strated to me the simplest and most in-
expensive radio receiver in the world.
Although generally cautious in the use of super-
latives, in this case I use them without fear of
contradiction. The cost of the receiver in ques-
tion is precisely nothing. It is exceedingly
compact; you could hide it under either half of
your mustache, although it might not be con-
venient to keep it there. It is portable; you can
carry it around the house, or outside, set it up
in an instant, and when you don't want it, it
disappears. It provides a loud speaker signal of
moderate intensity. The loud speaker is con-
tained in the set. There are no knobs, tuning con-
trols, or adjustments of any kind; a child can
operate this receiver just as well as a radio
engineer. It requires no antenna and no battery
or power supply of any description. The main-
tenance cost, it follows, is nil. In these respects
it is certainly the ideal broadcast receiver.
It has only two faults, which, in all honesty,
I shall now reveal. It will not receive any other
station than KDKA. The tone is decidedly thin.
The technical gentlemen of the Westinghouse
Company can produce any reasonable number of
these radio receivers on the transmitter grounds
on a moment's notice. All they do is to pick up a
nail or piece of metal and touch it to a spike in
one of the wooden poles which support the
antenna. Withdrawing the bit of metal slightly,
the experimenter pulls out an arc a quarter or
half inch long. He is thus drawing out of the air,
according to orthodox radio principles, a few
watts of the fairly considerable number which
KDKA is flinging prodigally over the Pennsylvania
hills. As this radio-frequency arc is modulated,
it sings shrilly in accordance with the voice or
music which is agitating the KDKA carrier at the
moment. It is a radio receiving set, with all the
virtues that I have claimed for it. And when you
are through with it you toss the nail away.
This receiver possesses one other convenience
which, as far as I know, is incorporated in no
other instrument of its class, and is found lack-
ing even in $3000 outfits built for barons and
millionaires. You can light a cigarette with it!
Operation of Broadcasting Stations
2O. FIELD STRENGTH MEASUREMENTS
MOST operators of broadcast transmitters
have only the vaguest sort of idea of
what their outfits are actually doing, in
the way of providing a signal for listeners, even
in their immediate neighborhoods. A broadcast-
ing station depends on its listeners just as much
as a newspaper depends on its readers, or a gas
or electric power company on its customers. The
newspaper comparison is closer from the practi-
cal commercial angle, while physically the gas or
power company analogy is quite exact. The
broadcast transmitter must provide a certain
radio-frequency pressure for the listeners whom
it wants to reach, just as the gas company must
maintain a certain gas pressure if it wants to sell
gas, and the electric power concern must keep a
fixed electric potential between its wires. The
difference is that the power and gas companies
know what that pressure is, whereas the broad-
caster generally does not. Yet there is no great
mystery about the matter. The field intensity
of a radio transmitter can be measured, not as
simply as gas and electrical pressures, but with
an amount of cost and trouble which is cer-
tainly not prohibitive considering the funda-
mental importance of the knowledge gained and
the fact that a large investment is often in-
volved. Every broadcast technician should at
least know the general theory of field intensity
measurements and calculations.
The principal articles in the I. R. E. Pro-
ceedings are the following:
Englund, C. R. : "Note on the Measurement of
Radio Signals," Vol. II, No. I, Feb., 1923.
Bown, Ralph; Englund, C. R.; and Friis, H. T.:
"Radio Transmission Measurements," Vol. n,
April, 1923.
Austin, L. W. and Judson, E. B.: "A Method of
Measuring Radio Field Intensities and Atmos-
pheric Disturbances," Vol. 12, No. 5, October,
1924.
Jensen, A. G.: "Portable Receiving Sets for
Measuring Field Strengths at Broadcasting
Frequencies," Vol. 14, No. 3, June, 1926.
Friis, H. T. and Bruce, E.: "A Radio Field-
Vacuum-Tube Voltmeter
Is hr hs
Ir = 120 X -
LOOP
•
(
!/.
—
1.0 mfcT
(cT
m
}
- '16V.--
(VWWWW^
36
6V.
Size of loop, 103 cm. square
No. of turns. 5
Inductance, 77 microhenries
Resistance.3.5 ohms
FIG. I
Strength Measuring System for Frequencies up
to Forty Megacycles." Vol. 14, No. 4, August,
1926.
For those who do not wish to consult the
sources listed above a brief outline of the sub-
ject is presented here.
A transmitting antenna, with a certain amount
of radio-frequency current flowing in it, sets up a
moving field of electric force which is expressed
in volts per meter, or in some more convenient
units, such as millivolts or microvolts per meter.
This simply means that if a receiving antenna is
put up within range it will be charged by that
field to a certain radio-frequency potential for
each meter of its electrical height. The field
strength of a 5-kw. broadcasting station, about
ten miles away across fairly good transmission
territory, may be of the order of 30 millivolts per
meter, to give a practical illustration. Then if a
listener puts up an outdoor antenna with an
electrical height of 3 meters, he will get 90 milli-
volts from that transmitter to put into his re-
ceiver. The electrical height is less than the
physical height (one-half is a common ratio).
It is a measure of electro-magnetic effectiveness
in transmission and reception. Its meaning may
be better understood after a study of the basic
absorptionless transmission formulas:
102
(0
where lr is the received antenna current in
amperes, Is the transmitter antenna current in
amperes, X wavelength in meters, f the fre-
quency in kilocycles, h, the effective or elec-
trical height of the receiving antenna, in meters,
hs the effective height of the transmitting an-
tenna, in meters, d the distance in meters be-
tween the antennas, and R is the resistance of
the receiving antenna.
The transmitting current may be measured
by means of a thermo-ammeter in the base of
the antenna. The wavelength and frequency
are known, if only because the Federal Radio
Commission and the Department of Commerce
insist on quite accurate data on this point. The
resistance of the receiving antenna at the partic-
ular frequency in question may be measured
by the added resistance method. (See Circular
of the Bureau of Standards, No. 74. "Resistance
Measurement.") The distance d is a factor which
may be set by placing a receiver a few wave-
lengths from the transmitter, and then \, will
be sufficiently high so that it may be measured in
the receiving antenna directly by means of a
thermo-galvanometer or thermo-milliammeter,
or the voltage across a receiving loop may be
found by means of a vacuum-tube voltmeter.
Thus the product of the two effective antenna
heights, hr hs may be calculated from (i), re-
written as follows:
losd R I,
hr hs — 1 (2 )
40 1C Is f
Of course this does not give us either hr or hs
individually. As stated before, h, may be ap-
proximated by taking half the physical height
of the flat-top of the receiving antenna above
ground, if it is well removed from absorbing
objects. Or, in the case of a loop antenna, it may
be calculated by a formula which is derived from
our knowledge of the mechanism of radio trans-
mission and the nature of radio-frequency
pick-up by a loop or coil antenna, which responds
to the electro-magnetic component of the wave.
With the loop turned end-on to the direction of
radiation, and the antenna effect disregarded,
the effective height is given by:
Area X Number of Turns , ,
„,.,*_ __ (})
Thus hr and hs may both be determined.
The quantity hs is also of importance in that
it is a measure of the radiating efficiency of the
transmitting antenna. This radiation resistance,
as it is called, is a part of the total resistance of
the antenna. An antenna, like any other energy-
converting device, has losses. The ohmic or heat
loss incidental to currents flowing in a conductor
is one of them. Then there are dielectric losses
in the ground or in objects near the antenna.
These are actual losses of energy similar to the
losses caused by windage, winding resistance,
and mechanical friction in an electric motor.
But an antenna is peculiar in that it has one
type of loss of energy which it is definitely
designed for, which is its reason for existence.
It radiates energy, which is purposely lost so
that it may be picked up elsewhere for the
communication of intelligence. The total power
dissipated in the antenna is given by:
JUNE, 1928
FIELD STRENGTH MEASUREMENTS
103
Pt = Is« Rt (4)
The radiated portion is given by:
Pr = U> Rr
Rr = 1600 !jf Ohms (5)
where Rt is the total transmitting antenna re-
sistance, R, is the radiation resistance, and h,
and >. are in the same units of length. Thus when
we have determined the radiation resistance of
the transmitting antenna by the procedure
which is outlined by formulas I to 5, we have
some idea of the energy radiated by the trans-
mitting antenna, which means that we know
the fundamental quantity in the physical func-
tioning of the station when it is "on the air,"
We know how much of the power we put into it
is getting away from the station.
A practical little summary of work in field
intensity determinations is the pamphlet by
R. O. Cherry, prepared under the direction of
Professor T. H. Laby, on "Signal Strength
Measurements oj 3/.0, Melbourne." The measure-
ing set consisted of a loop, a tuning condenser,
and a thermionic voltmeter to measure the
potential induced in the loop by the broadcast-
ing station. The voltmeter was an instrument
of the Moullin type, manufactured by the
Cambridge Instrument Company, using plate
rectification to cover a scale of 0-1.5 volts.
Cherry's pamphlet does not show the voltmeter
circuit, but this has been reproduced in Fig. I
of the present description, from page 35 of
Moullin's " The Theory and Practice oj High-
Frequency Measurements" (Charles Griffin &
Co., Ltd., London), an excellent work which
has been reviewed in this magazine. Moullin's
Fig. 25, added to Cherry's Fig. I, gives us our
Fig. i. In the manufactured form of the instru-
ment the plate battery is dispensed with and the
i.6-volt negative grid bias is secured from the
6-volt battery used to light the filament of the
tube. Aside from this battery the voltmeter is
self-contained. The calibration is stated to be
independent of frequency and the galvanometer
reads directly in volts, 1.5 volts r. m. s. being
full-scale. When the applied potential difference
exceeds 0.4 volt, grid current flows at the peak
of the positive half cycle, and the instrument
draws a slight amount of power, the apparent
resistance at full scale being of the order of 0.75
megohms, corresponding to a power absorption
of 2.5 microwatts. The voltmeter is used with
British valves intended for a 4-5 volt filament
potential, which is reduced to 3.5 volts in this
case, thereby prolonging the life of the valve
and the calibration of the voltmeter, barring
accidents, almost indefinitely.
The 3LO report starts off with Formula (3)
of the present discussion, followed by an expres-
sion for the field strength, whose equivalent is:
E • h, v , + wi L, (6)
K2
where E, in volts per meter, is the field strength
at the point of reception; V, in volts, is the
potential difference measured across the loop;
hr, in meters, is the effective height of the loop
w = 2xf, where f is the radiated frequency; L is the
inductance of the loop in henrys; and R is the
high-frequency resistance of the receiving cir-
cuit, at the frequency f.
It is easy to see how, according to (6) the
field strength, by definition, will equal the re-
ceived voltage divided by the effective height
of the receiver, but the origin of the square root
factor may not be clear. Cherry gives no explana-
tion, so it may be added that the expression with-
out the added factor would be true for an open
loop picking up a voltage from the transmitting
station in question, but in practice it is necessary
to tune the loop, as shown in Fig. i, both in
order to select the e. m. f. from the desired
station, and in order to get enough voltage to
measure. But then we are measuring the resonance
e. m. f. of the loop circuit, and this must be cor-
rected by -./!•• w2
^- before we can deduce the
field strength.
The next step is to measure or calculate the
inductance of the loop. For the calculation
process the reader is referred to the Bureau of
Standards circular cited above. If a calibrated
local oscillator is available, and the condenser
across the loop also has a known calibration,
the distributed capacity of the loop may be
determined, and the inductance is then easily
calculable from the wavelength formula:
X = 1.885 x IO'V/TC (7)
where C is the total capacity (loop capacity
plus condenser capacity).
Fig. 2 shows a curve of wavelength against
various capacities of the tuning condenser when
the loop circuit is tuned to different frequency
settings of the oscillator coupled to it. The
line being extrapolated, the point where it cuts
the X-axis (zero wavelength) gives the dis-
DISTRIBUTED CAPACITY OF LOOP
2000
° 1000
/
•^
^
S
/
/
S
^
! 0 100 200 300 400 500 600 700 80
CAPACITY MMFD.
FIG. 2
tributed capacity of the loop. In the case of the
3 LO experiment the wavelength was 371 meters,
and the loop capacity was found to be 65 micro-
microfarads, which, added to the condenser
capacity for resonance, gave a total capacity of
505 micro-microfarads, whereupon substitution
in (7) gives: _
371 = 1.885 X io'i/Lx 505 x 10 •»
L = 7.698 x lo-5 Henry
= 77 Microhenrys
The resistance of the loop, condenser, and
voltmeter circuit must also be measured.
Cherry gives the procedure, but instead of re-
peating it I shall refer those who have a practical
interest in the problem to Circular No. 74 again.
The mean of several measurements in the
particular example we are following was 3.5
ohms. A source of inaccuracy which must be
considered at this point is that the resistance of
the thermionic voltmeter is not quite constant,
introducing a variable loss, which Cherry be-
lieves is between 0.5 and 0.9 ohm equivalent
series resistance. This will result in a slightly low
value for the higher field strengths, but as such
measurements, made with a loop, are not good
to better than 5-10 per cent., a mean value for
the high-frequency resistance of the receiving
circuit is sufficient for practical purposes.
All the other quantities needed for the calcula-
tion, first of the effective height of the loop
(Formula 3), then of the field strength (Formula
6), are known. Using Formula 3, we may write:
371
both the length of the side of the loop, which,
squared, gives the area, and the wavelength,
being expressed in meters; the result gives h,,
also in meters, as 0.090. To get E from (6) we
w L
must find the value of -fr~; w is 2x f, and f is the
frequency corresponding to a wavelength of
371 meters; this may either be looked up in a
wavelength-frequency table or calculated from
the basic relationship that the frequency is the
velocity of light (3x10* meters per second)
divided by the wavelength, whence:
w = 2 x LjLJS? = 5.08 x ,0.
and =i = (5.08) (.0.) (77) do-*) _
R 3.5
So finally we get E - ; ^ — r - —
(0.09) (112) 10.1
This gives us the field strength in terms of the
reading of the thermionic voltmeter, divided by
a substantially constant factor, as long as the
same loop, condenser, and voltmeter are used,
and the wavelength remains the same. The loop,
of course, is turned to secure a maximum de-
flection for each observation. If the apparatus
were to be used for only one station, the wave-
length of which is fixed, the voltmeter scale
could be arranged to read the field strength di-
rectly.
In the case of 3 LO, the following field strengths
in m/v per meter were found, using the procedure
outlined:
DISTANCE DIRECTION
i Mile
5 Miles
10 Mites
North
400
90
East
350
60
30
Wed
200
50
25
From such data it is possible to draw contour
maps of the field pattern of a station, such as
those secured in the elaborate investigation of
the distribution of WEAF and WCAP (Bown and
Gillett: "Distribution of Radio Waves from
Broadcasting Stations over City Districts,"
Proc. 1. R. E., Vol. 12, No. 4, August, 1924).
Bown and Gillett used one of the short-wave
measuring sets developed by Bown, Englund,
and Friis, and with this more elaborate apparatus
were able to get down to field strengths of the
order of a fraction of a millivolt per meter;
some of their curves extend to a distance of over
a hundred miles from the transmitter. The simple
apparatus described by Cherry is, of course,
restricted to a much smaller radius, but it illus-
trates the principles involved just as effectively.
The contour lines in the case of 3 LO form a group
of quite regular concentric ellipses, which would
be expected with the transmitter located in fairly
open country. The pattern from a station
located, like the old WEAF, in the heart of a city
like New York, is far more irregular, naturally.
Within the radius of neglectable absorption
the product Ed (field strength times distance
from transmitter) is approximately a constant;
this relation may be used as a check on the ac-
curacy of the field strength measurements.
Goldsmith ("Reduction of Interference in
Broadcast Reception," Proc. I. R. E., Vol. 14,
No. 5 October, 1926) gives the following table of
program service as a function of field strength:
SIGNAL FIELD STRENGTH NATURE OF SERVICE
10.
loo.
1000.
volt per meter
volts per meter
volts per meter
volts per meter
volts per meter
Poor service
Fair service
Very good service
Excellent service
Extremely strong
Edgar Felix has pointed out that the commercial
value of a broadcast transmitter, other things
being equal, is a function of field distribution.
This is true, and, when the owners of stations
realize it, more field strength measurements will
be made in divers neighborhoods. If the field
strength is not being produced in the sections
where it is wanted, the artists and the ad-
vertisers might as well go home, and the studio
be converted into a salesroom for artificial
flowers.
The limitations of space will not permit a
longer technical discussion of the subject.
Readers who are interested beyond this point
are again referred to Moullin's book, in which
Chapter VIII (pages 218-254) 's devoted to a
thorough study.
The Listener's Point of View
HOW CAN GOOD RADIO PROGRAMS BE CREATED?
By JOHN WALLACE
IN THIS department last month we proposed
the question "Can the Broadcaster Improve
Broadcasting?" and averred that in our
opinion he could not and that the time was ripe
for him to call in outside help. The suggestion is
a sound one and we are further confirmed in our
conviction of its essential truth by our discovery
that the same idea occurred, at almost the identi-
cal time, to several other professional reformers
of radio.
Since we think the point is an important one
and worth acting upon, and since it is best em-
phasized by repeating it, we quote from two other
scribes. Mr. Zeh Bouck, in his estimable column
in the New York Sun said in part:
"Our asseveration that the program de-
partments of large broadcasting companies
were, in principle and practice, incapable
of turning out more than a small percentage
of meritorious programs — originality, inter-
est, intelligence and esthetics being the cri-
teria of merit — has aroused a certain amount
of controversial interest. The question arises,
if the program departments of the large
broadcasting companies should, as we have
suggested, be eliminated in some relatively
painless manner, who, then, should prepare
the programs? Or rather, let us say, conceive
the programs, for the actual preparation, the
manual labor, could still be left to the studio
hacks. There remain three possibilities. The
advertiser can prepare his own programs,
making broadcasting a section of his ad-
vertising department. Second, the advertis-
ing agency is a logical consideration, prepar-
ing material for broadcasting in a manner
comparable to the preparation of printed ad-
vertising. Both of these systems are in oper-
ation to-day, and are producing programs
notably superior to the rubber stamp variety
turned out by the broadcast organizations
themselves. . . .
"On the other hand, the program depart-
ment of the large broadcasting organization,
turning out programs by the hundreds, fitting
a Swiss cheese classic and a rather extenuated
ode to Persian rugs into pretty much the
same skeleton after the manner of Martin
Eden writing his pot boilers, necessarily ex-
hibits the creative talents of a child making
mud pies.
"There is still a third possibility which we
originally suggested a few weeks ago, namely,
the purchase by the broadcasting company
or advertising agency, for that matter, of
ideas and radarios submitted by free lances,
in much the same manner that stories are
submitted and bought by magazines. In
this manner, a wealth of new material and
ideas would supplement the rather wornout
traditions of radio Cook's tours and songs of
yesteryear.
"These ideas, and the radarios themselves
when necessary, could be readily adapted to
broadcasting by the station organization,
which is often as adept in the mechanics of
broadcasting as it is inept in creative bril-
liance."
Mr. Morris Markey, not a professional ob-
server of radio, but a writer of special articles,
leaped immediately to this same conclusion in a
story written recently for the New Yorker.
"A small amount of work is being done
among the four hundred employes of the
National Broadcasting Company in the way
of experimental programs. There have been
hesitant, and on the whole unsuccessful, efforts
to create visual images, of setting and atmos-
phere, through the loud speakers. And there
have been sporadic trials of dramatic episodes,
snatches of plays and such. But like most en-
terprises organized solely for the pursuit of
money, the broadcasting industry is con-
servative. An experiment itself, it looks upon
experiment in the entertainment it provides
as something to be avoided. It has failed to
recognize that radio has thus far produced
not one suggestion of showmanship. It has
failed to observe that the showmanship of
the microphone, when once it is developed,
will be a vastly different thing from the
showmanship of the camera or the stage.
The employes whose duty it is to keep the
performance going are, in the large part,
hacks. They are routine men who are not
hired for imagination or invention, but for
their ability to fill every hour on the air with
something or other, preferably of a revenue-
producing nature. There is not in all the radio
world a figure comparable to the producer
in the theatre or the director in the movies —
and most of the gods of the trade are un-
conscious, apparently, of their need for such
a figure. Vaguely it is realized that something
will have to be done about the programs, but
few in the industry appear to understand
that these programs must have the touch of
a creative person upon them."
How Long Can the Ballyhoo Last?
THE second big splurge of the Dodge
Brothers Company, its much touted Movie
Star Hour turned out to be "just another
program." The foregoing review is a decidedly
unfair one, for at the time we write, the program
referred to has not yet taken place and will not
for several days. It is to be made up — or at the
time you read this, was made up — of the voices
of Norma Talmadge, Charlie Chaplin, Douglas
Fairbanks, D. W. Griffith, John Barrymore, and
AMOS N ANDY; ALIAS CORRELL AND
GOSDEN
The former "Sam V Henry" team so popular
with listeners to WON have transferred their
attentions to the microphone of WMAQ of Chi-
cago where they are heard nightly at 7:11 P.M.
central time, except Sunday and Wednesday
104
Dolores del Rio. It required the usual million
miles or so of telephone wires, the conventional
thousand or so engineers, and of course the tril-
lion or so dollars of investment and commanded
the listening attention of every man, woman,
and child in the United States over the age of
thirteen months. And it served to convince this
particular reviewer that most of the individuals
heard had selected their profession with great
wisdom and ought to be encouraged to stick
to the silent drama. Mr. Barrymore, to be sure,
contributed an excellent reading of the Hamlet
soliloquy, but the only reward for listening to
the others was a satisfied curiosity concerning the
pitch of their voices.
Just to show us up as an inaccurate prognos-
ticator, that program may turn out to be a wow.
But it hardly seems likely. There is no reason
to expect that because Norma Talmadge is
perfectly entrancing on the screen her voice is
going to prove anything in our parlor. We
would be far more willing to lay a wager with
Lloyd's that she will be a fizzle. But we don't
intend to write indignant letters to the sponsor-
ing company arguing this point for they are just
as aware of it as we are. Our opinion of their
fancy program, and indeed the opinions of any
of our fellow scribes, mean quite nothing at all
to them. And rightly so: they are not concerned
with devising a good radio program but with
getting something up to ballyhoo. They have
craftily selected six of the biggest names in the
movie world. They will get countless miles of
newspaper space, probably not only in the radio
sections, but perhaps in the movie sections as
well, and even in the news columns and edi-
torial pages. In other words, though it costs them
a fortune to hire the movie stars and the broad-
casting facilities, they will probably get more
newspaper space than they could have paid for
with ten times the sum, and they'll get the air
advertising to boot.
Nobody, not even the querulous critics, actu-
ally got riled about their thousand-dollar-a-
minute Victory Hour; we were all too bowled
over with admiration of the really beautiful ad-
vertising coup that it was. But nobody pretends
that it ranked very high in entertainment. In a
" list of the best programs of the year it would
have placed well down in the second hundred.
The movie star hour will probably take even
lower rank.
The two programs mentioned have not been
the only Ballyhoo Hours in radio's history.
Others have been the inaugural hours of Palm-
olive, Wrigley and General Motors. Of any
Ballyhoo Hour this is true: the sponsor's interest
in the program is decidedly secondary to his
interest in the printed stuff it gives him a chance
to cook up and perchance, to have published.
In other words the program is no end in itself
but merely the excuse for deluging editor's desks
with mimeographed mouthings.
In some ways it is idle for us to rail at the
Ballyhoo Hour. It is both big business and good
business. If it appears to exploit the sucker strain
in the Americano the answer is that he likes to
have it exploited. But as a gent whose waking
hours are supposed to be concerned with the
vital matter of seeing radio programs improved
it is our bounden duty to eye such stuff aghast.
JUNE, 1928
THE LISTENER'S POINT OF VIEW
105
WE DO SOME EYEING AGHAST
OUR objection to the Ballyhoo Hour is pre-
cisely, that, while it doubtless does much
good for the advertiser, it does nary a bit of
good for radio. Furthermore it pains our frugal
soul to see so much mazuma spent in such a
wasteful way. Wasteful, as far as radio is con-
cerned, because after one of these hours is over
nothing remains, except perhaps an unpleasant
taste. Nothing has been contributed to the "art "
of broadcasting, no new precedent has been es-
tablished upon which bigger and better develop-
ments may be built. Suppose some of the fifty or
so thousand dollars that is commonly planked
down for one of these programs were used for
the employment of talented persons to create
something new — such as the Sound Drama
we suggested last month — that would be a
real step.
But such arguments can carry no weight. It is
too much to ask the advertiser to worry about the
future of the radio art. We shall have to search
another point of attack. Here's one: the novelty
of these Big Splurge, Ballyhoo programs can't
last forever. Since public interest in them is at
bottom simply curiosity concerning the amount
of money spent and the magnitude of the names
employed, each succeeding big splurge is going
to have to outdo its predecessor in order to pique
the jaded curiosity of that public. Eventually it
will be necessary to bill the crowned heads of
Europe and transmit the stuff over jewelled
platinum wires costing $9.85 an inch in order
to get a rise out of the radio editors. So the
Ballyhoo Program will very soon exterminate
itself.
However, there is still another reason why the
commercial broadcasters themselves ought to
take steps to eliminate the ballyhoo program
and that is that it doesn't serve to increase radio's
prestige very much. The Big Splurge program
attracts what the storekeeper knows as a Bar-
gain Day Crowd. The merchant, on the day of a
big sale, lures a lot of strangers into his store who
have never crossed its threshold before. Most of
them never will again; but a few of them may
observe that his everyday merchandise is of
good quality and may become habitual custom-
ers.
The Big Splurge program sucks in perhaps a
couple million listeners who ordinarily disdain
radio, refuse to purchase receivers and are only
submitting to the pleas of friends to "come over
and play a hand of bridge and listen to Such and
Such." This is a swell chance to corral these pros-
pective customers and make "em come back for
more. But the Pomp and Circumstance Program
is prone to have one or other of the two following
effects: A. The program turns out to be merely
ordinary as entertainment, thus confirming the
transient listener's opinion that radio is a
moron's pastime or; B. Great musical artists are
lavished with such profusion (as in some Victor
Hours) that his follow-up essay at listening is
dimmed to nothingness by contrast.
A Thursday Evening on the Blue
Network
PERHAPS our eternal weeping in these
columns over the fact that radio so seldom
attains great art, and so frequently suc-
ceeds in being bad art, conveys the impression
that we never get any enjoyment out of it at all.
Not so. For instance last night, a Thursday eve-
ning in March:
Arming ourself against the ordeal with an
entertaining novel, we plugged-in KYW, the local
vendor of the Blue Network's
wares, at 7:00 o'clock. Central
Time. Well we didn't get in
any reading during the first half
hour. O. Henry's story, "The
Clarion Call," was being presented
in the "Re-Told Tales" series.
Our listening was mostly a matter
of conscientiousness for the first
ten minutes, but after that the
thing carried itself along for the
remainder of the half hour and
stacked up as one of the best
radio plays we have heard. A
two-character play, making use of
a conventionally far-fetched O
Henry plot it was "put across" by
the expectionally fine voice acting
of the villain. Sorry we don't re-
member his name; the good job of
script preparation was done by one
Henry Fisk Carlton and the pro-
duction was directed by a Gerald
Stopp.
At 7:30 when the Ampico Hour
came on we commenced to look for
our place in our book — for we
have heard some rather dismal
Ampico Hours. But unfortunately
for novel reading the program
opened with some of Smetana's
music for "The Bartered Bride"
which we like too much to miss.
Then Marguerite Volavy, playing the piano both
in solo and in concerto, kept our willing atten-
tion for the rest of the program.
We got in a little reading during the Maxwell
House concert, but not much. This program is
always craftily arranged and expertly presented.
The "Old Colonel March" and the "Indian
Love Lyrics" we could have got along very nicely
without, but Richard Crooks called for sitting
up and taking notice when he sang the "Prize
Song" and the Siciliana from "Cavalleria."
This grand singer — deservedly popular — even
AT STATION WGR, BUFFALO
Nancy Cushman, daughter of Howard B. Cushman, director
of the station, confiding to the world that she is two years old.
" M icrophone fright " does not seem to bother her
put beauty in the banal "Little Bit of Heaven."
The orchestra kindly included a grand waltz
from Komzak's " Bad'n Mad'l'n."
The Continental's program followed at 9:00
o'clock. This hour, too, is an ever reliable one,
made up, as you know, of opera selections and
not exclusively of the hackneyed ones. However,
as two hours of attentive listening is enough for
anybody to put in consecutively, we at this point
took up our book and enjoyed the perfectly swell
radio voices of Astrid Fjelde, Frederic Baer, et
cie., as a rather vague background.
THE WBAL ENSEMBLE
This group is heard every Friday night from WBAL Baltimore. The group includes (left to right):
Michael Weiner, violinist-conductor; Leroy Evans, pianist and Samuel Maurice Stern 'cellist. Mi-
chael Weiner is the orchestral supervisor. WBAL is one of the few stations that takes its music seriously
SO MANY good words must be said for this
month's supply of records that we feel we
ought to offer a word of explanation at the
start. Readers grow suspicious when any reviewer
waxes consistently eulogistic. They picture all
critics as mean creatures, shriveled in body and
soul, who starve themselves on a diet of vinegar
and sour grapes that they may the better enjoy
the flaws which they pick, gloating over the bones
of their victims. It fills us with joy to find a col-
lection of records so good that we can honestly be
lavish with praise. Such is the present collection.
Good and Popular
In the Sing Song Sycamore Tree and Four
Walls played by the Ipana Troubadours directed,
of course, by S. C. Lanin (Columbia). What is so
rare as a really good tune? Two of them, of
course. And here they are! Superbly played by
the Troubadours and expertly sung by Scrappy
Lambert.
The Whip and We'll Have a New Home in the
Morning played by Nat Shilkret and the Victor
Orchestra (Victor). Lyrics that are different,
harmony that's grand, and an orchestra that's
infectious.
Can't Help Lovin' Dat Man and Make-Believe
played by Ben Bernie and His Hotel Roosevelt
Orchestra (Brunswick). Smooth — in the best
Bernie tradition, and with Vaughn De Leath
and Scrappy Lambert doing neat vocalizing.
Say So! and Oh Gee! — Oh Joy! played by Ben
Selvin and His Orchestra (Columbia). Yes, and
we'll add a few more exclamation marks just for
good measure!!!!
Mary Ann and // / Can't Have You played
by Hal Kemp and His Orchesta formerly of
the University of North Carolina. (Brunswick).
Where they got their M. A. (musical acrobat)
degrees, no doubt. No? Well, they got very
proficient somewhere.
Call of Broadway and Without You Sweetheart
played by Vincent Lopez and His Casa Lopez
Orchestra (Brunswick). Mediocre music made
more than a little danceable by a swell orchestra.
Sensation Stomp and Whiteman Stomp played
by Paul Whiteman and His Orchestra (Victor).
Whiteman conducts a class in orchestral gymnas-
tics. Proving what?
Who Gives You All Your Kisses played by the
Troubadours (Victor). As usual you can safely
put your money on the Troubadours. They will
even carry the weak sister on the other side.
What Are We Waiting For played by Edwin J.
McEnelly's Orchestra.
Tin Pan Parade played by the Troubadours
(Victor) is another prize winner; Chloe, on the
reverse, by the All Star Orchestra is just an also-
ran.
Somebody Lied About Me and Chloe played
by the Colonial Club Orchestra (Brunswick).
Something old, nothing new, something bor-
rowed, something blue.
I Ol' Man River and Can't Help Lovin' Dat Man
played by Don Voorhees and His Orchestra
(Columbia). Two good numbers from the popu-
lar Ziegfeld musical comedy, "Show Boat."
My Ohio Home and Here Comes the Showboat
played by Jean Goldkette and His Orchestra.
(Victor). The second number is novel — and
excellent.
Rose Room and Golden Gate by Herb Wiedoeft
and His Orchestra (Brunswick). Musical
publicity for the Land of Sunshine.
For My Baby and The Man I Love by Leo
Reisman and His Orchestra and Fred Rich and
His Hotel Astor Orchestra, respectively (Colum-
bia). F. f. f. or fine for foxtrotting.
Tin Pan Parade and / Told Them All About
You sung by Ford and Glenn (Columbia).
The
^Month's New
Phonograph
Easily the best of the recent vocal records.
Sweetheart of Sigma Chi and Charmaine sung
by Allen McQuhae (Brunswick). A better tenor
voice than you usually hear warbling these grand
old favorites!
In an Oriental Garden and Roses for Remem-
brance played by the Anglo-Persians under the
direction of Louis Katzman (Brunswick). Mr.
Katzman is the best musical gardener we know.
Lolita and Yesterday played by the A. and P.
Gypsies under the direction of Harry Horlick
(Brunswick). Very nice indeed.
More or Less Classic
Lucia — Sextette (Donizetti) and Rigoletto —
Quartet (Verdi). (A) sung by Galli-Curci, Homer,
Gigli, De Luca, Pinza, Bada; (B) sung by Galli-
Curci, Homer, Gigli, De Luca (Victor). What's
good enough for Gatti-Casazza is good enough
fo'r us.
Song of the Flea (Moussorgsky) and Barbiere
Di Siviglia — La Calunnia (Rossini). Sung by
Feodor Chaliapin (Victor). The name of this
abysmal basso is sufficient guarantee of satis-
faction on any record. This in particular is de-
lightful.
Meistersinger-Kirchenchor (Wagner) and Meis-
tersinger-Wach' auf! Es Nahet Gen Den Tag
(Wagner). Sung by the State Opera Chorus of
Berlin, with Orchestra, conducted by Leo
Blech (Victor). A very effective imported re-
cording of this beautiful choral music from
Wagner's merry opera.
Pagliacci-Son Qua! and Pagliacci-Andiam!
(Leoncavallo). Sung by the Metropolitan Opera
Chorus, with Metropolitan Opera House Or-
chestra, conducted by Giulio Setti (Victor).
More choral music that is worth several times
the price of admission.
The Masked Ball— Is It Thou? (Verdi) and
Pagliacci — Prologue (Leoncavallo) Sung by
Heinrich Schlussnus (Brunswick). A competent
baritone presents these two operatic selections.
Andante Canlabile (Tschaikowsky) and Can-
jonetta (Tschaikowsky). Played by Albert
Spalding (Brunswick). Creating one paramount
impression: that of charming grace.
Chanson Arabe (Rimsky-KorsakofT — Kreisler)
and Le Deluge (Saint-Saens). Played by Toscha
Seidel (Columbia). Mr. Seidel is assisted in the
first selection by Max Rabinovitch at the piano,
and in the second by Emanuel Bay — because
it is the custom and not because this talented
violinist needs assistance.
Ave Maria (Carnevali) and Stabat Mater
(Pergolesi). Sung by Giuseppe Danise (Bruns-
wick). A rich baritone voice lending itself very
successfully to ecclesiastical music. The ac-
companiment of chimes in the Ave Maria is
particularly nice.
Traviata — Prelude (Verdi) and Sylvia Ballet —
Cortege de Bacchus (Delibes). Played by the
Victor Symphony Orchestra directed by Rosario
Bourdon (Victor). No home is complete with-
106
out these familiar but none-the-less lovely
selections.
Poet and Peasant Overture, Parts I and 2 (von
Suppe). Played by the Brunswick Concert Or-
chestra (Brunswick). Part i is the dreamy poet;
part 2: the rollicking peasant . . . but you know
it; it has appeared on every "pop" concert pro-
gram for years.
Emperor Waltj and Wine, Woman and Song
Walt% (Strauss). By Jacques Jacobs' Ensemble
(Columbia). Here are the waltzes of yesteryear!
Jolly Fellows Waltf (Wollstedt) and The
Skaters (Waldteufel). Played by the Brunswick
Concert Orchestra under the direction of Louis
Katzman (Brunswick). Sweet memories of the
old skating rink and the creaking calliope! The
tunes are the same, that's all!
Recent Album Record Sets
WAGNER BAYREUTH FESTIVAL RECORDINGS
(Columbia). In one album, Masterworks Set
No. 79) the Columbia Phonograph Company
offer the following excerpts from four Wagnerian
operas: (i) Parsifal: Transformation Scene,
Act i ; Grail Scene, Act I ; Flower Maidens'
Scene, Act. 2; Prelude, Act 3; and Good Friday
Music, Act 3; (2) Rheingold: Entry of the Gods
into Valhalla; (3) Die Walkure: Ride of the
Valkyries: (4) Siegfried: Forest Murmurs, Act 2;
Prelude, Act 3 ; Fire Music. The orchestra is that
of the Bayreuth Festival, over which three fa-
mous conductors share the honors of wielding the
baton. They are Dr. Karl Muck, one time direc-
tor of the Boston Symphony Orchestra, Siegfried
Wagner, and Franz von Hoesslin. The recordings
were made in Bayreuth during actual perform-
ances of the operas in the summer of 1927 and
have been approved by Siegfried Wagner.
We will not go into a detailed description of
the records. You either know and love the music
or you don't. If you do, you will want the album
anyway. If you don't, you should get the album
and learn to know the music.
The set contains eleven double-faced records
and costs J 16.50.
Symphony No. 4, D Minor, (Op. 120) by Robert
Schumann. Played by the New Symphonic Or-
chestra, Berlin, under the direction of Hans
Pfitzner. Complete on three and a half double-
faced records (Brunswick).
Schumann conceived the Fourth Symphony as
a whole rather than as four distinct movements.
The same thematic material runs through the
entire work. The symphony is very colorful, very
warm and full of lovely melodic phrases. The
fourth movement is particularly beautiful.
Concerto for Organ and Orchestra, F Major,
(Op. 4, No. 4) by George Frederic Handel.
Played by Walter Fischer accompanied by or-
chestra. Complete on two double-faced records.
Concerto for Organ and Orchestra, F Major
(Op. 777) by Joseph Rheinberger. Played by
Walter Fischer accompanied by orchestra. Com-
plete on three double-faced records. (Brunswick).
The Brunswick-Balke-Collender Company
would have acted more wisely had they separa-
ted these two concertos rather than offered them
together in one album. The Rheinberger Con-
certo, which is in spots uninteresting to the
point of dullness suffers sadly by contrast with
the exquisite Handel composition. Both con-
certos are beautifully played by the famous
organist of the Berlin Cathedral.
Death and Transfiguration (Op. 24) by Richard
Strauss, played by the State Opera Orchestra
under the direction of the composer. Complete
on three double-faced records (Brunswick).
This tone poem dealing with the struggle be-
tween life and death is one of the most powerfully
dramatic of modern orchestral compositions.
"Radio Broadcast's" Directory of Vacuum Tubes
'PHE table below is as complete as is possible to make
•*• it and should be a constantly useful reference for all
radio workers. The data on some Western Electric tubes
are included because some of our readers live in Canada
and in other countries where tubes of this manufacture
are available. We have followed the RCA-Cunningham
tube terminology; other manufacturers make types of
tube similar in each class, although each manufacturer
has his own terminology. The reader who desires to use
a CeCo tube for example, need only ask his dealer or the
manufacturer for a CeCo of the 201-A type, etc. The
same follows naturally for any of the vacuum tubes in
the classifications below made by Arcturus, Sovereign,
Sylvania, Marathon, Gold Seal, Sonatron, Kellogg,
Magnetron, Speed, and others.
AVERAGE CHARACTERISTICS OF RADIO VACUUM TUBES
GENERAL
DETECTION
AMPLIFICATION
MODEL
USE
CIRCUIT
REQUIRE-
MENTS
INTER-ELECTRODE
CAPACITIES IN MMFD.
FILAMENT COLD
"A"
SUPPLY
FILAMENT! FILAMENT
TERMINAL] CURRENT
VOITAGE IIAMPERES)
DETECTOR
GRID RETURN
LEAD TO
GRID
LEAK
MEGOHMS
DETECTOR
>' BATTERY
VOLTAGE
DETECTOR
PLATE CURR'T
MULIAMPERES)
AMPLIFIER
'B'BATTEKY
VOLTAGE
AMPLIFIER
C" BATTERY
VOLTAGE
AMPLIFIER
PLATE CURRENT
(MILLIAMP£RES>
A.C.PLATE
RESISTANCE
(OHMS)
MUTUAL
CONDUCTANCE
MICROMHOS
VOLTAGE
AMPLIfl'TOfl
FACTOR
MAXIMUM
UNDIS10RTED
OUTPUT
(MILLIWATTSI
Ml
WD-11
Same as bel
w, except
or base
which 1
old UV ty|
CX-12
WX-12
Detector or
Amplifier
Transformer
Coupling
G-F6:G.P5.5;P.F7.5
OrrC.llliV
Storage 2 V
1.1
.25
*F
3 to 5
22^1045
1.5
90
135
4^4
lOfc
2.5
3.5
15,500
15,000
425
440
6.6
66
7
35
CX-112A
UX-1I2A
Detector or
} Amplifier
Transformer
Coupling
G-F9;G-P11; P-F7.5
Storage 6 V
5.0
.25
«F
3 to 5
45
1.5
90
135
V
5.5
7
5.300
5.000
1,500
1,600
8
a
30
120
C-299
UV. 199
•M
e as be
iw, except
for basi
which i
old UV ty|
1
CX-299
UX-199
Detector or
Amplifier
Transformer
Coupling
G-F 3.6; GP3.5; PF4.5
OryCelUJV
Stwigel V.
3:0
3.3
.060
.063
*F
2 to 9
45
1
90
«i
23
15,500
425
6.6
7
CX-300A
UX-200A
Detector
Tnr,sl. or
(esisCouptinj
G-F 3 4; G-P8.8; P-F 1.5
Storage 6 V
5.0
.25
-.F
2 to 3
• 45
1.5
Following UX-200 A characteristics
apply only for Detector connection
30,000
666
20
—
ex-sou
UX-201 t
Detector or
Amplifier
Transformer
Coupling
G-F5.8; G-P10.1: P-F 6.1
Storage 6 V
5.0
.25
+ F
2to9
45
1.5
90
135
V
2.5
3
11,000
10.000
725
800
8
8
15
55
CX- 322
UX-222
Radio Freq.
» Amplifier
Special
Shielding
G-P 0.025
SSSAl
3.3
.132
—
—
—
—
135
ij"
1.5
850,000
350
300 n
CX-322
UX-222
Audio Freq.
(Amplifier
Resistance
Coupling
Dr,l.«U'iV
Stout. «V
3.3
.132
—
-
-
—
180}
li°
.3
160,000
400
60
—
UX-226
CX- 326
Amplifier
A.C. Filament
Type
Transformer
Coupling
G-F3.65; G-P8.2; P-F 2.1
Tnnsformff
1.5V.
1.5
1.05
' -
- -
—
—
90
135
180
6
Jl
3.5
6
T5
9,400
7.400
7,000
875
1.100
1.170
8.2
8.2
8.2
20
70
160
C-327
UY-227
Detector A.C.
Heater Type
Transformer
Coupling
G-F3.6; S-P3.7: P-F2.75
Transformer
2.5V.
2.5 H
1.75
K
2-9
ti
45
90
2
7
Following UT-227C
apply on y for Detec
haracterietics
or connection
10,000
8,000
800
l.OOO
8
8
—
CX-340
UX-240
Detector or
Amplifier
Resistance
Coupling
G-F3.4; G-P 8.8; P-F 1.5
Storage 6V
5.6
.25
*F
2 to 5
1351
180!
"0.3
g
135 I
180?
?
.2
.2
150,000
150.000
200
200
30
30
—
CX-112A
UX-112*
I Power '
' Amplifier
No LS.C.
Required
G-F9; G-P 11; P-F 7.5
Trlnslwmtr
5*.
5.0
.25
—
—
—
—
135
1575
10}
7
9.5
5.000
4,700
1.600
1700
8
8
120
195
CX-220
UX-120
Power
Amplifier
No L.S.C.
Required
G-F4.5; G-P5.4; PF4.4
OrrCtlMlV.
StorijH V.
3.0
3.3
.125
.132
—
—
— '
'—
135
22^
6.5
6,300
525
3.3
110
CX-371 A
UX-171 A
Power
Amplifier
LS.C.
;wr
G-F 6.8; G P 9.5; P-F 6.5
Stouj* 6 V.
Tunsfuimfr
5V.
5.0
.25
—
-
—
—
£
180
'M
40 j
10
16
20
2.500
2,200
2,000
1,200
1,360
1,500
3.0
3.0
3.0
130
330
700
tX-310
UX-210
Power
Amplifier
LS.C.
G-F 7; G P 8; P-F 7
Transformer
;sv
7.5
1.25
—
—
—
—
18,
fg
»
I
6.0OO
5,'000
i:4318
1.550
1.600
1.600
1
Ijlo
CX-350
UX-250
Power
Amplifier
LS.C.
G-P 8.7
Transforms
7.5V.
7.5
1.25
—
—
—
—
Jio1
1!
70
84
!!
55
55
2,100
i.eoo
1
3.8
y
43;iio°
AVERAGI
; CHA
RACTERISTICS
DF V
r'ESTE
RN ELECTRI
C TUBES
"N,"
215-A
Detector or
Amplifier
Transformer
Coupling
G-F 4.4; G-P6; P-F3.8
—
1.0
0.25
+ F
2-9
45
1.0
67
6.0
1.0
20,000
300
6
8
"y"
1020
Amplifier
Resis. or
Impedance
Coupling
—
—
2.0
0.97
—
—
—
—
130
1.5
075
60.000
500
30
4.2
"L"
216A
Amplifier
Transformer
Coupling
—
—
5-6
1.0
—
—
-
—
130
9.0
8.0
6.000
980
5.9
60
"0"
104 D
Amplifier
Transformer
or Imped.
Coupling
c,-rt.-i.G-r3.4(>,p-r&o
—
•
4-3
10
—
—
—
—
130
22 j
20.0
2,200
1.100
2.4
145
205 D
Power
Amplifier
Transformer
or Imped.
Coupling
-
4.5
1.6
—
—
—
—
350
22.S
33
3,500
2,000
7
890
SPECIAL PURPOSE TUBES
MODEL
USE
CIRCUIT
REQUIREMENTS
BASE
MAXIMUM
OVERALL
HEIGHT
MAXIMUM
OVERALL
DIAMETER
PURPOSE
CHARACTERISTICS
CX-380
UX-280
Full Wave
Rectifier
Full-Wave
Circuit
Large
Standard
UX Base
•r
•A"
Rectification in
Eliminators
Filament Terminal Voltage.. 5 Volts >
Filament Current 2 Amperes (R M g
A.C.PIatt Voltage 300 Volts I
(Max-per Plate) '
Max.D.C.Outpu
D.C.Outpu
oft
Current (both Plates) 125 Milltamperes
Voltage at Max. Current as applied to filter
pica! rectifier circuit 260 Volts
CX- 381
UX-281
Half Wave
Rectifier
Half or Full
Wave Circuit
Large
Standard
UX Base
•*•
«"
Rectification in
Eliminators
Filament Terminal Voltage_,7.5 Volts ^
Filament Current 1.25 Amperes \ R M S
A.C.PI»t« Voltage 750 Volts j
(Maximum)
A.C. Plate V
DC. Output
D.C. Output
oltage
Rtcomminded Minimum
_ 650.. 750 Volts
Current
Voltage as applied to filter of typical r
ectifier circuit. .620. .620 Volts
CX-374
UX-874
Voltage
Regulator
Series
Resistance
Large
Standard
UX Base
•»"
2ft"
Constant
Voltage
Device
yg^^^S^SS Operating Vo,t.g. 90Vo,t,D.C.
different vaiuesofB-current St.rt.ng Voltage.. _125VoltsD.C.
are supplied Operating Current 10-50 Milltamperes
C-376
UX-876
Current
Regulator
(Ballast Tube)
Transformer
Primary of
65 Volts
iKiM.
Standard
Mogul Type
Screw Base
a"
4"
Constant
Currant
Device
Designed to insure onstant input
)per»ting Current 1.7 Amperes
Mean Voltage Drop 50 Volts
Permissible Variation.... tlOVolts
despite fluctuation in line voltage
C-386
UX-886
Current
Regulator
(BillaslTube
Transformer
Primary of
65 Volts
for use on
1 IS Volt Lin*
Standard
Mogul Type
Screw Base
a"
2|V
Con start
Current
Device
Designed to Insure onstant input Operating Current 2.05 Amperes
to power operated adio receivers Mean Voltage Drop _ 50 Volt*
despite fluctuation In line voltage Permissible Variation 1 10 Volts
C-377
Protective
Tub.
—
Double £
Contact
Bayonet
Auto.Typ«
•A"
•f
Current
Limiting
Device
Used in'B'Battery circuits to
prevent excessive current resulting
from short-circuit which might
damage tubes or wiring
Voltage D
rop Across
_ Half
Filament
2.5
45
FilanSa
5 At 20 Mitliamperes DC
90 At90 Milliamperes DC.
t U) Note Other use of this Radiotron above'below)
• Inner Grid -I1/? Volts, Outer Grid + 45 Volts. 0.15 Milliamperes
0 Outer Grid -l1^ Volts( lnnerGrtd+22!^ Volts,6 Milliamperes
1 Applied thru plate coupling resistance of 250.0OO Ohms
A Connection to shell ol base for third terminal which is the lead
to mid-point of filament
Note : All grid voltages are given
with respect to cathode or
negative filament terminal
Maximum values not to
be exceeded
Except for half ampere filament.UX-1 12 and UX- 1 71 characteristics are identical respectively to UX-1 12-A
and UX-171-A.
K Cathode
H HeaterVoltage
LSC.. Loud Speaker Coupling,consisting of either Choke Coil and By-Pa&s Condenser or Output Transformer oll'l
orstep down ratio.recom mended wherever plate current (aC-)exceeds lOmilliamperes.
M With a screen-grid tube, on account of circuit I imitations, the actual voltage amplification obtainable does
not bear as high a relation to the voltage amplification factor as in the case of three element tubes.
107
Manufacturers' Booklets
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
12 E A DERS may obtain any of the booklets listed below by use-
ing tbe coupon printed on this Page. Order by number only,
1. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS— A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
1 5. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE C9NpENSERS — A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their application to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
17. BAKELITE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SH9RT-WAVE WAVE-
METER — Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
positions in the circuit where audio-frequency chokes may
be used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio- frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED.
51. SHORT-WAVE RECEIVER — Constructional data on a
receiver which, by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY — A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL. INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA — Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. RESISTANCE COUPLING^— A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION.
63. FIVE-TUBE RECEIVER — Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
70. IMPROVING THE AUDIO AMPLIFIER — Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used.
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM — A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
82. SIX-TUBE RECEIVER — A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams,
and templates for the construction and assembly of socket
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Panel layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequency
transformers of special design. KARAS ELECTRIC COMPANY.
85. FILTER — Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A socket
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimental
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blueprint and necessary
data, for building an eight-tube receiver. THE GEORGE W.
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER — Data and blue prints
are given on the construction of a short-wave transmitter,
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES.
90. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification are
given. ALDEN MANUFACTURING COMPANY.
93; B-SOCKET POWER — A booklet giving constructional
details of a socket-power device using either the BH or 313
type rectifier. NATIONAL COMPANY, INCORPORATED.
94. POWER AMPLIFIER — Constructional data and wiring
diagrams of a power amplifier combined with a B-supply
unit are given. NATIONAL COMPANY, INCPRPORATED.
101. USING CHOKES — A folder with circuit diagrams of
the more popular circuits showing where choke coils may
be placed to produce better results. SAMSON ELECTRIC
COMPANY.
22. A PRIMER OF ELECTRICITY — Fundamentals of
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
26. DRY CELLS FOR TRANSMITTERS — -Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS— Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE — Battery life curves with general
curves on tube characteristics. "BURGESS BATTERY COM-
PANY.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
32. METERS FOR RADIO — A catalogue of meters used in
radio, with diagrams. BURTON-ROGERS COMPANY.
3^. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. WHY RADIO Is BETTER WITH BATTERY POWER — Ad-
vice on what dry cell battery to use; their application to
radio, with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR— Information on the care of
vacuum tubes, with notes on how and when they should be
reactivated. THE STERLING MANUFACTURING COMPANY.
69. VACUUM TUBES — A booklet giving the characteris-
tics of the various tube types with a short description of
where they may be used in the circuit. RADIO CORPORA-
TION OF AMERICA.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS — A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new 4Oo-mil!iampere rectifier tube. CARTER RADIO
COMPANY.
102. RADIO POWER BULLETINS — Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
103. A. C. TUBES — The design and operating character-
istics of a new a. c. tube. Five circuit diagrams show how
to convert well-known circuits. SOVEREIGN ELECTRIC &
MANUFACTURING COMPANY.
In sending the coupon below, make sure that your
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41. BABY RADIO TRANSMITTER OF gxn-pEK — Descrip-
tion and circuit diagrams of dry-cell operated transmitter.
BURGESS BATTERY COMPANY.
42. ARCTIC RADIO EQUIPMENT — Description and circuit
details of short-wave receiver and transmitter used in
Arctic exploration. BURGESS BATTERY COMPANY.
58. How TO SELECT A RECEIVER — A commonsense
booklet describing what a radio set is, and what you should
expect from it, in language that any one can understand.
DAY-FAN ELECTRIC COMPANY.
67. WEATHER FOR RADIO — A very interesting booklet
on the relationship between weather and radio reception,
with maps and data on forecasting the probable results.
TAYLOR INSTRUMENT COMPANIES.
73. RADIO SIMPLIFIED — A non-technical booklet giving
pertinent data on various radio subjects. Of especial in-
terest to the beginner and set owner. CROSLEY RADIO COR-
PORATION.
76. RADIO INSTRUMENTS — A description of various
meters used in radio and electrical circuits together with a
short discussion of their uses. JEWELL ELECTRICAL IN-
STRUMENT COMPANY.
78. ELECTRICAL TROUBLES — A pamphlet describing
the use of electrical testing instruments in automotive work
combined with a description of the cadmium test for stor-
age batteries. Of interest to the owner of storage batteries.
BURTON ROGERS COMPANY.
95. RESISTANCE DATA — Successive bulletins regarding
the use of resistors in various parts of the radio circuit.
INTERNATIONAL RESISTANCE COMPANY.
96. VACUUM TUBE TESTING — A booklet giving pertinent
data on how to test vacuum tubes with special reference to
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT
COMPANY.
98. COPPER SHIELDING — A booklet giving information
on the use of shielding in radio receivers, with notes and
diagrams showing how it may be applied practically. Of
special interest to the home constructor. THE COPPER AND
BRASS RESEARCH ASSOCIATION.
99. RADIO CONVENIENCE OUTLETS — A folder giving
diagrams and specifications for installing loud speakers in
various locations at some distance from the receiving set.
YAXLEY MANUFACTURING COMPANY.
105. COILS — Excellent data on a radio-frequency coil
with constructional information on six broadcast receivers,
two short-wave receivers, and several transmitting circuits.
AERO PRODUCTS COMPANY.
106. AUDIO TRANsppRMER — Data on a high-quality
audio transformer with circuits for use. Also useful data on
detector and amplifier tubes. SANGAMO ELECTRIC COMPANY.
108. VACUUM TUBES — Operating characteristics of an
a.c. tube with curves and circuit diagram for connection
in converting various receivers to a.c. operation with a
four-prong a.c. tube. ARCTURUS RADIO COMPANY,.
109. RECEIVER CONSTRUCTION — Constructional data on
a six-tube receiver using restricted field coils. BODINE
ELECTRIC COMPANY.
no. RECEIVER CONSTRUCTION — Circuit diagram and
constructional information for building a five-tube set
using restricted field coils. BODINE ELECTRIC COMPANY.
ill. STORAGE BATTERY CARE— Booklet describing the
care and operation of the storage battery in the home.
MARKO STORAGE BATTERY COMPANY.
1 12. HEAVY-DUTY RESISTORS — Circuit calculations and
data on receiving and transmitting resistances for a variety
of uses, diagrams for popular power supply circuits, d.c. resis-
tors for battery charging use. WARD LEONARD ELECTRIC
COMPANY.
113. CONE LOUD SPEAKERS — Technical and practical in-
formation on electro-dynamic and permanent magnet type
cone loud speakers. THE MAGNAVOX COMPANY-
114. TUBE ADAPTERS — Concise information concerning
simplified methods of including various power tubes in
existing receivers. ALDEN MANUFACTURING COMPANY.
115. WHAT SET SHALL I BUILD? — Descriptive matter,
with illustrations, of fourteen popular receivers for the home
constructor. HERBERT H. FROST, INCORPORATED.
104. OSCILLATION CONTROL WITH THE "PHASATROL"—
Circuit diagrams, details for connection in circuit, and
, ,
specific operating suggestions for using the "Phasatrol"
as a balancing device to control oscillation.
INCORPORATED.
ELECTRAD,
.
1 16. USING A B POWER UNIT — A comprehensive book-
let detailing the use of a B power unit. Tables of voltages —
both B and C — are shown. There is a chapter on trouble-
shooting. MODERN ELECTRIC MFG. Co.
117. BEST RESULTS FROM RADIO TUBES — The chapters
are entitled: "Radio Tubes," "Power Tubes," "Super De-
tector Tubes," "A. C. Tubes," "Rectifier Tubes," and
"Installation." GOLD SEAL ELECTRICAL Co.
118. RADIO INSTRUMENTS. CIRCULAR "J" — A descriptive
manual on the use of measuring instruments for :very radio
circuit requirement. A complete listing of models for trans-
mitters, receivers, set servicing, and power unit control.
WESTON ELECTRICAL INSTRUMENT CORPORATION.
120. THE RESEARCH WORKER — A monthly bulletin of in-
terest to the home constructor. A typical feature article
describes the construction of a special audio amplifier —
AEROVOX WIRELESS CORPORATION.
121. FILTER CONDENSERS — Some practical points on the
manufacture and use of filter condensers. The difference be-
tween inductive and non-inductive condensers. POLYMET
MFG. CORP.
122. RADIO TUBES — Specifications and operating charac-
teristics of vacuum tubes. Twenty-four pages. E. T. CUN-
NINGHAM, INC.
123. B SUPPLY DEVICES — Circuit diagrams, characteris-
tics, and list of parts for nationally known power supply
units. ELECTRAD, INC.
124. POWER AMPLIFIER AND B SUPPLY — A booklet giving
several circuit arrangements and constructional information
and a combined B supply and push-pull audio amplifier, the
latter using 210 type tubes. THORDARSON ELECTRIC MFG. Co.
125. A. C. TUBE OPERATION — A small but complete
booklet describing a method of filament supply for a.c. tubes.
THORDARSON ELECTRIC MFG. Co.
126. MICROMETRIC RESISTANCE — How to use resistances
for: Sensitivity control; oscillation control; volume control;
regeneration control; tone control; detector plate voltage
control; resistance and impedance coupling: loud speaker
control, etc. AMERICAN MECHANICAL LABORATORIES.
1 08
RADIO BROADCAST ADVERTISER
109
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THORDARSON
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The Radio Broadcast
LABORATORY INFORMATION
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to
that time was printed. Last month we printed an index covering the sheets published from
August, 1927, to May, 1928, inclusive.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. I to 88, can be secured from the Circulation Department,
Doubleday, Doran & Company, Inc., Garden City, New York, for $1.00. Orders for the
next set following can also be sent. Some readers have asked what provision is made to
rectify possible errors in these Sheets. In the unfortunate event that any serious errors do
occur, a new Laboratory Sheet with the old number will appear.
— THE EDITOR.
No. 193
RADIO BROADCAST Laboratory Information Sheet
June, 1928
'Motorboating"
HOW IT CAN BE PREVENTED
MANY amplifiers at times show a tendency to
"motorboat" due generally to interaction
coupling between stages, due to common coupling
in the plate-supply unit. This effect can generally
be eliminated by using the circuit shown on this
Laboratory Sheet. This circuit was suggested in a
recent bulletin from the E. T. Cunningham Com-
pany.
The an ti- motor boa ting circuit consists of a net-
work of condensers and resistances connected
between the power unit and the B-plus detector
terminal on the radio receiver. The effect of this
circuit apparently is to eliminate coupling effects
at the low frequencies at which such effects are most
troublesome. The circuit has been used with good
results in the Laboratory, in connection with
resistance -coupled amplifiers which generally show
the strongest tendency to motorboat. but the cir-
cuit may be satisfactorily used with any type of
amplifier.
It is not difficult to add this circuit to any existing
receiver installation. To do this it is simply neces-
sary to connect the resistance K in series with the
lead connecting between the B-plus detector
terminal on the receiver and the B-plus detector
terminal on the power
unit. One 2.0-mfd. con-
denser Ci must then
be connected between
the B-plus terminal
and the B-minus on
the receiver and
another condenser C>
connected between the
B-plus detector and
minus B terminal on
the power unit. It is
preferable to locate
trhe resistance at a
point close to the re-
ceiver rather than near
the power unit.
The value of the resis-
tance depends to some
extent upon the char-
acteristics of the receiver and the power unit.
With some amplifiers we have found a value
of 10,000 ohms to be satisfactory, and with other
amplifiers, a resistance of 50,000~to 100,000 ohms
was required to prevent motorboating. A value
of a.bout 50,000 ohms seems to be satisfactory in
most cases.
ftMlio Recwver
1
8- CWt
>B
HM
—
i- B*Qet
Power Unit
No. 194
RADIO BROADCAST Laboratory Information Sheet
June, 1928
Push-Pull Amplifiers
HOWLING
PUSH-PULL type amplifiers in many cases
exhibit a tendency to howl at some audio fre-
quency due to feedback through the interelectrode
capacity of the tubes. When this occurs it is obvi-
ously impossible to obtain satisfactory operation
from the amplifier. The howling in push-pull ampli-
fiers can generally be readily prevented by con-
necting a choke coil or resistance at the point
marked X in the circuit diagram. When construct-
ing an amplifier of this type it is wise to include such
a choke or resistance in the circuit; no by-pass
condenser should be placed across the unit.
The inclusion of choke or resistance in this circuit
will not affect the quality for this circuit does not
have to carry any audio- frequency currents. In some
instances it will be found necessary to prevent howl-
ing to include also a choke coil in the lead from
the center tap of the output transformer and the
B-plus terminal ot the plate supply.
If a resistance is used in the grid circuit it should
have a value of about 50,000 ohms. Since it does
not have to carry any current, any ordinary grid
leak type of resistance unit may be used. The chokes
used may be any type with an inductance of about
10 henries or more. The primary of an old audio-
frequency transformer might be used in the grid
circuit but is not satisfactory for inclusion in the
plate circuit between the center tap of the output
transformer and the plate supply for when con-
nected at this point, the choke must carry the plate
current of the two tubes, which may be enough to
burn out the windings of an ordinary audio trans-
former. Use at this point some device designed to
carry 50 or 60 milliamperes. The circuit given on this
sheet also shows the use of a resistance Ri to supply
C bias to the two tubes. Its value, depending upon
the type of tubes used, is given below
Type of Tube Ri
"112-A 750 ohms
171-A 1000 ohms
210 11 00 ohms
Input
Transformer
RADIO BROADCAST ADVERTISER
111
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WIRELESS SPECIALTY APPARATUS COMPANY
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112
RADIO BROADCAST ADVERTISER
The Best
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k Standard '
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Sets
No. 195
RADIO BROADCAST Laboratory Information Sheet
June, 1928
A Resistance-Coupled Amplifier With Screen-Grid Tubes
CONSTRUCTIONAL DATA
February, 1927, RADIO BROADCAST re-
•*• ported some experiments made in the Labora-
tory on the use of the screen-grid tube in audio-
frequency and radio- frequency amplifiers, and
in the article there appeared a circuit diagram
of a resistance-coupled, audio- frequency amplifier
using two screen-grid tubes. Many letters have been
received requesting constructional data on this
amplifier and we have therefore reprinted the cir-
cuit diagram on Laboratory Sheet No. 196 and the
list of parts necessary to construct the amplifier
appears at the end of this Sheet.
The publication of this circuit diagram and list of
parts should not be taken to indicate unqualified
endorsement of the amplifier for its high voltage
gain of 2200 (the voltage gain of an average two-
stage transformer coupled amplifier is 250) in
some cases will prove more of a disadvantage rather
than an advantage. The disadvantage or a high
gain audio-frequency amplifier will become evident
when an attempt is made to operate it from a B-
power unit. When an ordinary amplifier is used
with a plate-supply unit which provides hum-free
operation no difficulty may ensue; but when this
same supply is connected to a high-gain, screen-
grid amplifier, the .hum is greatly magnified and
may be of entirely too high a value. If the screen-
grid tubes are operated from batteries, however,
this amplifier will give very satisfactory results.
To construct this amplifier the following parts are
necessary:
Ri, 0.25-Megohm Resistors
/?s, 2.0-Megohm Resistors
/?:t, 20-Ohm Filament Resistors
R\, 4-Ohm Resistor
/?s, 0.1 -Megohm Resistor
Ci, 0.01-Mfd. Fixed Condensers
Cj, 4.0-Mfd. Fixed Condensers
Cst 2.0-Mfd. Bypass Condensers
Three Sockets
Binding Posts
No special care is required in the construction of
this amplifier although it is wise to arrange the lay-
out so that the various grid and plate leads are
short. The condensers C» and the resistor R<, are in-
corporated in the circuit to prevent the amplifier
from motorboating. This circuit will also help to
keep the hum low if the device is operated from a B-
power unit.
A frequency characteristic curve of this amplifier
made in this Laboratory showed it to be flat from
100 to 10,000 cycles.
* 196 RADIO BROADCAST Laboratory Information Sheet June, 1928
Circuit of a Resistance-Coupled Screen-Grid Amplifier
+O -O +0 -O +O
C Supply
B B+ B+ B+ B+
Pet. 45 135 Power^
6 Supply
No. 197
RADIO BROADCAST Laboratory Information Sheet
Amplification. Constant
June, 1928
HOW IT MAY EASILY BE MEASURED
IT IS not difficult with simple apparatus to
measure the amplification constant of any tube
The important apparatus required to make such a
test are two accurate resistances, one variable, the
other fixed, and a milliammeter capable of carrying
the normal plate current of the tube under test.
The circuit diagram to be followed in making this
test is given here. The following parts are used in
the circuit:
EC — C-battery with" a value correct for the tube
under test. Eb — B-battery with a value correct for
the tube under test. Ea — Source of filament voltage.
E — 45 volt B-battery. Ri — Filament rheostat. Rs —
Accurate 10-ohm resistor. Rj — Accurate variable
resistor, having a maxmum value of 300 or 400 ohms.
I — Milliammeter having a maximum range of
about 20 milliamperes. K — Key to open and close
the circuit.
The important resistor in this circuit is Ri which
must be calibrated. A good potentiometer may be
used, provided it is supplied with a dial so that the
amount of resistance included in the circuit can be
calculated. For example, if the potentiometer has a
resistance of 400 ohms and the dial reads from 0 to
100 then each degree would include 4 ohms.
The test is conducted as follows. With K open,
adjust EC and Eb so that the tube is being operated
under the correct conditions of grid and plate volt-
ege. Note the plate current reading. Now depress
K and note the change in the reading of the milliam-
meter. Adjust Ri so that as the key is opened and
closed no change takes place in the reading of the
milliammeter. When resistor, Ri, has been adjusted
so that the plate current remains constant, cal-
culate the amount of resistance at Ri, included in
the circuit. Divide this resistance by 10, the value of
R>, and the quotient will be the amplification con-
stant of the tube.
EXAMPLE: A 201 -A type tube is being tested and a
balance is obtained when there are 83 ohms in-
cluded in the circuit at RI. Dividing Si by 10 we
get 8.3, the amplification constant of the tube.
RADIO BROADCAST ADVERTISKR
113
Concentrated
Effort!
IN specializing on and perfecting con-
densers and resistors which have stood
up under every test made to deter-
mine their worth, the Aerovox Wireless
Corp. has attained a goal made possible
only by perfect co-ordination, co-oper-
ation, and concentration of every ele-
ment ill an organization devoted exclu-
sively to the production of high Quality
condensers and resistors.
78 WASHINGTON ST.
BROOKLYN, N. Y.
the Code
Wireless or Morse— at home with the
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better method for self -instruction
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other instrument. Avail your-
self of the TVleplpx for a quick mastery of the code. Write
for booklet UK. TKI.HI'I.KX CO.. 7<t Cortlandt St., N*w York.
BROADCASTING FROM THE INSIDE
EVKRV nth in RADIO BROADCAST appears the departments
"As the Broadcast rr Sees It." written hy Carl Drt-her. ono of
tin- iM'si known broadcast engineers in the country. Alive with
humor, news, apt and searching couim>'nt. Mr. Drcher's writings
have bet-nine r.ne of the most popular features of radio writing any-
where. Are you reading it? Subscribe by the year and make sure of
not missing a single issue. Mail your check for $4.00 to Subscrip-
tion Department. Doubleday, Doran & Co., Inc., Harden City, N. Y.
PARALLEL PLATE FEED
TYPE 369 IMPEDANCE
A unit suitable for use in
parallel plate feed systems.
Price $5.00
Are you troubled with motor-
boating in your audio frequency
amplifier — or perhaps you have
purchased a pair of really good
audio frequency transformers and
after placing them in use, find
that results are not quite up to
your expectations? If your tubes
and plate supply are functioning
properly your trouble can, in
most cases, be eliminated by the
use of parallel plate feed. A
folder describing the advantages
of this system will be sent on
request.
GENERAL RIDIO
We welcome your correspondence in regard* to technical problems. Bulletin
No. 929, describing our complete line of Radio parts, will be sent on request.
30 State St., Cambridge, Mass.
274 Brannan St., San Francisco, Calif.
Tills Is a good time to sukseribe for RADIO BROADCAST
Through your dealer or direct, by the year only S4.00
DOUBLEDAY. DORAN & COMPANY, Inc., Garden City, N. Y.
RADIO PANELS
BAKELITE— HARD RUBBER
Cut, drilled and engraved to order. Send rough sketch
for estimate. Our complete Catalog on Panels, Tubes iind
Rods— all of genuine tiakelite or Hard Rubber — mailed
on request.
STARRETT MFG. CO.
521 S. Green Street Chicago, 111.
Fixed Voltage ES22I*1
Variables exist in any radio circuit. You
correct them by changing the controlling
resistance. If you want fixed voltages, use
the
B»i — *^flP
Adjusting
For best performance yonr tubes require a va-
riable filament control to supply the definite
€-urrt nt th«-y need, despite "A" battery varia-
€-urrt n , spite "A" battery
tions. AMPER1TE is the only self-adjuslinR and
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Orderbv name. Accept nothing else.PriccSl . 1O
im.unt.-d (in U. S. A.) For sale by all dealers.
Write for FHKE "AMPKR1TE BOOK" of sea-
son's bust circuit* and latest construction data.
Adilrtss Dept. R.B.-6.
RADIALL COMPANY
FROST-RADIO
Frost Variable High
Resistances
Think of a variable high resistance with a marvel-
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without wear, due to roller contact arm. N'o jerks —
no jumps — no dead spots — no sudden increases or
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tion. Has Bakelite shell and cover, and engraved
Baktrlite pointer knob. Adopted as standard by
leading set manufacturers, and countless thousands
arc in use in home built sets. Supplied in two or
three terminal type, in wide range of resist :nu ix
from 2,000 to 500,0x0 ohms, and with or without
switch. 2 or 3 Terminal Type, less switch, $1.75.
2 or 3 Terminal Type-, with switch, $2.10.
HERBERT II. FROST, INC.
Main O/icf.t ami Factory
Elkhart. In. I.
114
RADIO BROADCAST ADVERTISER
A New A C Transformer
with terminals for use with all types of
Wiring Harnesses
Here is the latest A C success in the Dongan
Approved A C line No. 6570, built into a
crystalized lacquered case, is equipped with
terminals for use with the new wiring har-
nesses. Designed to operate with 4 UX ia6,
i UY227 and i UX 171 power amplifier tubes.
Also equipped with lamp cord and plug out-
let for B-eiiminator as well as tap for control
switch. Price $6.50.
A Complete Line of Approved
A C and Output Transformers
By-Pass and Filter Type
Condensers
for Set Manufacturers
and Custom Set Builders
The reason you can expect real engineering
help as well as par in modern design and con-
struction is due to the fact that Dongan's en-
tire radio business always has been devoted
exclusively to the interest of the set manu-
facturer.
Ask for information and prices, on any de-
sired type, direct from Dongan to you.
See the Dongan Parts Exhibit at the R. M. A. Show
DONGAN ELECTRIC MFG. CO.
2991-3001 Franklin St Detroit, Michigan
V ' TRANSFORMERS of MERIT for FIFTEEN YEARS .
Jenkins £ Adair
Condenser Transmitter
For Broadcasting, Phonograph
Recording, and
Power Speaker Systems
THIS transmitter is a small condenser which
varies its capacity at voice frequency, and
is coupled direct into a single stage of ampli-
fication, contained in the cast aluminum case.
The output, reduced to 200 ohms, couples
to the usual input amplifier. The complete
transmitter may be mounted on the regulation
microphone stand. It operates on 180 v. B and
6 or 12 v. A battery.
This transmitter contains no carbon, and is
entirely free from background noise. Its yearly
upkeep is practically nothing. It is extremely
rugged, and will withstand hard usage.
Price, complete with 20 ft. shielded cable,
$225.00 F.O.B. Chicago.
J. E. JENKINS & S. E. ADAIR, Engineer.*
I.'.IMI N. Dearborn Parkway,
Chicago, I '. S. A.
Send for our bulletins on Broadcasting
Equipment
No. 198 RADIO BROADCAST Laboratory Information Sheet June, 1928
The Screen-Grid Tube as an R. F. Amplifier
CALCULATING GAIN
T3ROBLEM: — Suppose that we have a radio-
* frequency amplifier connected as indicated in
the figure and that a screen-grid tube is used. How
can we calculate the amplification that can be
obtained?
SOLUTION: — To solve the problem we must make
use of the tube constant known as the mutual
conductance, which, for the screen-grid tube, has a
value of about 350 micromhos or 0.000350 mhos.
The mutual conductance Gm by definition,
where Cm is the mutual conductance in mhos; 7»c
is the alternating current flowing in the plate circuit;
Eg is the alternating voltage impressed in the
grid; transposing this equation we get
across the input Eg. Transposing equation (4) to
get this ratio we obtain
Et
= Gm x Z
(5)
This equation shows that the gain of this circuit
using a screen-grid tube is simply equal to the
mutual conductance of the tube in mhos, times the
effective impedance of the tuned circuit.
Therefore, if we know the impedance into which
the tube is working, we can, by multiplying the
impedance by Gm, obtain the amplification. If the
tuned circuit at resonance has an effective imped-
ance of 100,000 ohms then the amplification would
be
Amplification =0.000350 X 100,000
=35
/ac = Gm % Es
(2)
The voltage Et across the tuned circuit is equal
to the impedance of the circuit Z times the current
through it £t - /ac x Z (3)
and therefore
Et = Cm x Es x Z
(4)
The amplification of the circuit is equal to the
voltage across the output Et divided by the voltage
No. 199 RADIO BROADCAST Laboratory Information Sheet
Current
June, 1928
ITS DIRECTION OF FLOW
THE direction of flow of current around a
*• simple circuit consisting of a battery and a
resistance is generally considered to be as indicated
by the solid arrows in sketch A on this sheet. As
indicated, the current is thought of as flowing put
of the positive terminal of the battery, through the
resistance and into the negative terminal of the
battery. ,
Now let us look at the circuit of a vacuum tube,
as indicated in sketch B. In this circuit we would
assume that the current would flow as indicated by
the solid arrow, i, e., out of the positive terminal
through the tube and into the negative terminal
just as it did in circuit A. However, we know that
the filament of the tube is the electron-emitting
substance and that the electron flow is from the
filament to the plate. Apparently we have two
currents flowing in the cir-
cuit, and this has led some
experimenters to believe
that there were two distinct
currents flowing in the cir-
cuit, one the battery current
and the other the electron
current. This is not so and
there is only one current I «jT—
flowing in the circuit, the
electron circuit. (A)
The idea that the elec-
tric current flows from the
positive to the negative
originated before anything
was known about elec-
trons. This direction of (low
has since been proved
to be wrong. It is now
realized that an electric cur-
rent is actually a flow of
electrons and that elec-
trons, being negatively
charged, flow toward the
point of positive po-
tential. Therefore the actual
flow of current in the
tube circuit B and the
battery circuit A is as in-
dicated by the dotted arrows.
Fortunately the incorrect assumption that was
made years ago for the direction of the flow of cur-
rent is not important in the solution of electrical
problems so long as we remain consistent regarding
the direction inlwhich the current is assumed to flow.
Many meters used in electricity are marked
with plus and negative signs and the winding of the
meter is arranged so that the pointer on the meter
will deflect in the right direction when the positive
terminal of the meter is connected to the more
positive part of the circuit.
No. 200
RADIO BROADCAST Laboratory Information Sheet June, 1928
Resistors
DETERMINING WHAT SIZE TO USE
TN CHOOSING a resistance for any particular
•*• purpose it is necessary to determine the value
required, the current it must carry and then from
these two facts determine the wattage rating re-
quired. The chart published on this sheet will prove
useful to determine:
(a) the wattage rating a resistor must have to
carry a given current
(fr) the current a resistor, of given wattage rat-
ing, will carry
The curve is plotted to cover resistors up to
10,000 ohms and wattage ratings up to 5 watts.
EXAMPLE: A resistor is to be used to supply
C-bias to a 171-A type tube. The plate current of the
tube (which must flow through the resistor) is 20
milliamperes. The required C-bias voltage is 40
volts. What value of resistance and what wattage
rating should the resistor have?
To calculate the required value of resistance we
use Ohm's law.
Referring to the chart below, we find that the
vertical line corresponding to 2000 ohms crosses the
horizontal line corresponding to 0.020 amperes
(20 milliamperes) at the point indicated between
the curves of 1.0 and 0.25 watt resistors. In such a
case we must, of course, always use the larger size
and therefore in this case we should use the 1.0-
watt resistor.
Resistance
_ Voltage
"Current in amperes
40
~ 0.020
= 2000 ohms
6000 8000 10.000 12,000 14,000 16,000
RESISTANCE IN OHMS
RADIO BROADCAST ADVERTISER
115
STATEMENT OF THE OWNERSHIP. MANAGE-
MENT. CIRCULATION, ETC., required by the Act
of Congress of August 24, 1912, of RADIO' BROAD-
CAST, published monthly at Garden City, New York
'or April 1, 1928. State of New York, County of
\assau.
Before me, a Notary Public in and for the State
and County aforesaid, personally appeared John J.
Hessian, who, having been duly sworn according to
law. deposes and says that he is the treasurer of
Doubleday, Doran & Co., Inc., owners of Radio Broad-
cast and that the following is, to the best of his
knowledge and belief, a true statement of the owner-
ship, management (and if a daily paper, the circula-
tion), etc.. of the aforesaid publication for the date
shown in the above caption, required by the Act of
August 24, 1912, embodied in section 411, Postal
Laws and Regulations, printed on the reverse of this
form, to wit:
1. That the names and addresses of the publisher,
editor, managing editor, and business managers are:
Publisher Doubleday, Doran & Co., Inc., Garden City,
N. Y.; Editor. Willis Wing, Garden City, N. Y.;
Business Managers, Doubleday, Doran & Co., Inc.
Garden City, N. Y.
2. That the owner is: (If owned by a corporation,
its name and address must be stated and also im-
mediately thereunder the names and addresses of
stockholders owning or holding one per cent, or more
of total amount of stock. If not owned by a cor-
poration, the names and addresses of the individual
owners must be given. If owned by a firm, company,
or other unincorporated concern, its name and ad-
dress, as well as those of each individual member,
must be given.) F. N. Doubleday, Garden City,
N. Y.; Nelson Doubleday, Garden City, N. Y . :
S. A. Everitt, Garden City, N. Y.: Russell Double-
day. Garden City, N. Y.; George H. Doran, 244
Madison Avenue, N. Y. C. ; George H. Doran, Trustee
for M. N. Doran, 244 Madison Avenue, N. Y. C. :
lohn J. Hessian, Garden City, N. Y.; Dorothy D.
Babcock, Oyster Bay, N. Y.: Alice De Graff, Oyster
Bay N. Y.; Florence Van Wyck Doubleday, Oyster
Bay, N. Y. ; F. N. Doubleday or Russell Doubleday,
Trustee for Florence Doubleday, Garden* City, N. Y.;
Janet Doubleday, Glen Cove, N. Y.; W. Herbert Eaton,
Garden City, N. Y.: S. A. Everitt or John J. Hessian,
Trustee for Josephine Everitt. Garden Citv. N. Y.:
William |. Neal. Garden City. N. Y.: Daniel W.
\vc. Garden Citv, N. Y.; E. French Strother, Garden
City N. Y : Henry L. Jones, 244 Madison Ave.,
N Y C : W. F. Etherington, 50 East 42nd St.,
N Y C. : Stanley M. Rinehart. Jr., 1192 Park Ave.,
N. Y. C.
3. That the known bondholders, mortgagees, and
other security holders owning or holding I per cent.
or more of total amount of bonds, mortgages, or
other securities are: (If there are none, so state.)
NONE.
4. That the two paragraphs next above, giving the
names of the owners, stockholders, and security hold-
ers, if any, contain not only the list of stockholders
and security holders as they appear upon the books
of the company but also, in cases where the stock-
holder or security holder appears upon the books of
the company as trustee or in any other fiduciary re-
lation, the name of the person or corporation for
whom such trustee is acting, is given; also that the
said two paragraphs contain statements embracing
affiant's full knowledge and belief as to the circum-
stances and conditions under which stockholders and
security holders who do not appear upon the books
of the company as trustees, hold stock and securities
in a capacity other than that of a bona fide owner;
and this affiant has no reason to believe that any
other person, association, or corporation has any in-
terest direct or indirect in the said stock, bonds, or
other securities than as so stated by him.
5. That the average number of copies of each issue
of this publication sold or distributed, through the
mails or otherwise, to paid subscribers during the
six months preceding the date shown above is
(This information is required from daily publications
^Signed) DOUBLEDAY, DORAN & COMPANY, INC.
By John J. Hessian, Treasurer.
Sworn to and subscribed before me this 15th day of
March. 1928.
[SEAL] (.Signed) Frank 0 Sullivan
(My commission expires March 30, 1928.)
Why not subscribe to Radio Broadcast? By the year only $4.00;
or two years $6.00, saving $1.40. Send direct to DouhKlay,
Doran tf Company, Garden City, New York.
1010 .NVENTlOoVc
* WANTED ^*
en > new b.ok
__ >entions. Oen'l
Concentrate oil the NEEDED
The world needs radii inventions. One idea may make yo
ey Raymond F. Tales contains a list ol 99 needed Riidi
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Mil IITIIKK NKEIIKII 1\\K\TIIINS
ate also described, mcludniq tutomotiie. Electrical. tuto. Meebanieel, Chemi-
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Do You Buy
Satisfaction?
Pattern No. 139
Higk Rantancc Voltmeter— For the Set
Owner
After all, it is the satisfaction you expect to derive from
it that causes you to buy any product. It may be satisfac-
tion obtained from the use of the device, or satisfaction
from pride of ownership.
Owners of the Jewell Pattern No. 139 high resistance
voltmeter for the set owner find satisfaction both from use
and pride of ownership, for the use of this instrument brings
assurance of accurate results and its appearance will be an attractive addition to any radio set.
Pattern No. 139 is of the D'Arsonval moving coil type with high internal resistance requiring
little current draw, with results much more accurate than obtained with the ordinary type of
voltmeter. The range is 0-300 volts. Movement parts are all silvered, and the scale is silver
etched with black characters.
Description and price of this instrument are given in a special circular No. 1 103. Write for a copy.
Jewell Electrical Instrument Company
1650 Walnut Street, Chicago
"28 Years Making Good Instruments"
Follow the Radio Leaders!
Those who know the value of microme
resistance— precisely matched to radio a
tions — always specify not merely variabl
sistance but —
etric \
ondi- I
le re-
TJ
Ret;. U. S.
ROBERT S. KRUSE
Consultant and Technical Writer
103 Meadowbrook Road, West Hartiord, Conn.
Hartford 4S32J
Tlili t> a gooJ time to tukxrtkc /or
RADIO BROADCAST
Through your dealer or direct, by the year only $4.00
^ ^^ ^^t^i
The Improved
HAMMARLUND
Equalizing Condenser
(ireatly simplified, more compact
and more sturdily constructed than
the previous model.
The fixed plate of brass, the mica
dielectric and the movable phos-
phor-bronze spring plate are firmly
riveted to the Bakelite base and
cannot short. The adjusting
screw gives a wide capacity var-
iation.
Always
Improving!
EVER seeking ways to better its products
and to reduce their cost — that is the
Hammarlund purpose.
But quality first is the Hammarlund ideal,
steadfastly maintained for 18 years.
Whatever radio parts you may need —
condensers, coils, chokes, dials or shields,
ask for Hammarlund first.
It is the safe way to insure satisfaction.
Interested in low-wave reception?
Write for special folder.
HAMMARLUND MFG. CO.
424-438 West 33rd Street New York
ammarjund
PRODUCTS
116
RADIO BROADCAST ADVERTISER
New Aero Circuits
for Either Battery or A. C. Operation
Proper constants for A. C. operation of the Im-
proved Aero-Dyne 6 and the Aero Seven have been
studied out, and these excellent circuits are now
adaptable to either A. C. or battery operation. A. C.
blue prints are packed in foundation units. They
may also be obtained by sending 250 for each direct
to the factory.
Aero Universal
Tuned Radio Frequency Kit
Especially designed for the Improved Aero-Dyne 6.
Kit consists of 4 twice-matched units. Adaptable to
2OI-A, igp. 112, and the new 240 and A. C. Tubes.
Tuning range below 200 to above 550 meters.
Code No. U-I6 (for .0005 Cond.) $15.00
Code No. U-163 (for .00035 Cond.) 15.00
Aero Seven
Tuned Radio Frequency Kit
Especially designed for the Aero 7. Kit consists
of 3 twice-matched units. Coils are wound on Bake-
lite skeleton forms, assuring a 95 per cent, air dielec-
tric. Tuning range from below 200 to above 550
meters. Adaptable to 2io-A, 199, 112, and the new
240 and A. C. Tubes.
Code No. U-1Z (for .0005 Cond.) . . . $12.00
Code No. U-1Z3 (for .00035 Cond.) 12.00
You should be able to get any of the above
Aero Coils and parts from your dealer.
If he should be out of stock order
direct from the factory.
AERO PRODUCTS, INC.
1772 Wilson Ave. Dept. 109 Chicago, 111.
Radio
Convenience
Outlets
Wire your home for radio. These out-
lets fit any standard switch box. Full
instructions with each outlet.
No. 135— For Loud Speaker $1.00
No. 137— For Battery Connections 2.50
No. 136 For Aerial and Ground 1.00
With Bakelite Plates
Now furnished with a rich satin brown Bakelite
plate, with beautiful markings to harmonize, at
25 cents extra. See Illustration.
At Your Dealers
Yaxley Mfg. Company
Depl. B, 9 So. Clinton Si.
Chicago, III.
A-FILTER
Here is a new kind
of DRY and HUM-
LESS A-FILTER,
ready to hook onto
any 6 volt charger,
to convert your fila-
ment supply to A. C.
No harnesses, no new tubes required.
Clip this ad, and send with your
name and address today for pam-
phlet B-S.
TORE DEUTSCHMANN CO.
S CAMBRIDGE, MASS. /
The
By RAYMOND TRAVERS
LIFE on Teraina (Washington Island)
was one of complete detachment from all
the rest of the world. After a thrilling
ride through the surf and a safe landing on the
beach, a strange sense of having been abandoned
comes over you. This is followed, after a few days
by a feeling of emancipation. At last life is freed
from its great complications, and the mad
existence of the cities is but a hazy thing of the
past. Living is simplified to the fundamentals.
Sleep is not only a matter of the nights but is
indulged in during the hot noon-day. Food comes
from cans without fuss or garnish. Eating is a
necessity — not a habit. Everyone has work to
perform and in so doing is called upon to exercise
feats of ingenuity beyond belief. There isn't
any assistance around the corner. Further and
further into the background of the mind fades
the worlds beyond the horizon, and greater be-
comes the content with the life at hand.
The steamer from Honolulu arrived about
every four months (once it was nine!) and
brought mail, excitement, and grief, most times.
For the few days the little ship lay off the island,
unloaded its cargo of food and supplies, and took
aboard the tons of copra we had laboriously gath-
ered, conditions ashore were in a state of crazy
confusion. The mail had to be sorted for matters
of great importance requiring immediate reply;
the supplies to be checked and examined, some
to be returned or complained about; sometimes
distinguished guests to be entertained, when
every minute was so vital to personal affairs.
At last the sailing hour arrives, the ship dis-
appears, and the last surf boat is hauled ashore.
There are weary sighs, some cursing, a few drinks
of gin and cocoanut, and a prayer that the
blooming ship will never return!
Tabueran (Fanning Island) and Teraina
(Washington Is-
land), are Brit-
i s h possessions,
situated one
thousand miles
directly south of
Honolulu, about
three degrees
north of the
Equator, and five
thousand miles
west of Panama.
The finest copra
in the world is
nutted here, but
never in large
quantities, be-
cause the major
parts of both
islands are wild,
prohibiting maxi-
mum crops and
efficient collec-
tion. In 1917 an
Englishman was
sent from Londrn
to place Washing-
ton Island on
a more modern
operating basis
and increase pro-
duction.
At Fanning is
located the relay
station on the
ON THE sands behind the coral reefs of
Washington Island, in the Pacific South
Seas, a thousand miles south of Honolulu
and five thousand miles west of Panama, an j
audion bulb was picked up some years ago. j
There was a radio telegraph station at Wash- j
ington Island, and R. A. Travers was the 1
operator. He saw the audion bulb, recognized j
the handiwork of the inventor, and that |
night put the bulb in the mail, with the fol- j
lowing letter:
WASHINGTON ISLAND.
VIA HONOLULU AND FANNING ISLAND
December i, 1919.
Dr. Lee DeForest,
New York City.
Dear Doctor DeForest:
I am sending you by parcel post an inter-
esting valve 1 believe to be one of you pre-war
1 types. . . . This valve traveled many miles \
\ through the Pacific ocean, bobbed over a |
I coral reef, and came to rest on the sands of J
I this island. . : . Washington island is a wee spot '
| in the wide Pacific, having less than a dozen
1 miles of coast. . . . From wreckage picked up
I from time to time, it appears drifting objects
I come from the eastward. ... I believe this |
I valve will be of interest in your collection.
R. A. TRAVERS.
The foregoing paragraphs appeared in an
article in the November, 1025, RADIO BROAD-
CAST as introduction to part of the history of
Dr. Lee DeForest. Mr. Travers here writes his
side of the story and gives an interesting
description and more details of this "wee
spot in the wide Pacific" where the "lost
audion" was found.
Pacific Cable Board's
WASHINGTON ISLAND IN THE SOUTH PACIFIC
Here the author found the audion which
had drifted thousands of mile's — from where:
Canadian-Australian
lines. The cable
from Fanning to
Bamfield, British
Columbia, is the
longest in the
world, running
from the warm
waters of the
tropics into the
slate gray,
choppy and cold
shallows of the
north — five thou-
sand miles! All
important com-
munications be-
tween England
and the Colonies
were routed over
this cable, and so
we find one of the
notorious Ger-
man raiders ter-
rorizing the Smith
Pacific, slipping
ashore at Fan-
ning, and with
some well placed
dynamite, en-
larging the area
covered by the
cable buildings.
Off-shore the ca-
ble was cut. This
may have had
RADIO BROADCAST ADVERTISER
111
BKACH
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Approved by
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ENGINEERS AND MANUFACTURERS
NEWARK N J U.S.A.
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THE HAVEN OF A SEA-GOING
AUDION
(continued from page 116)
something to do with the fact that in May, 1917,
I left San Francisco with two 3 kw. wireless
sets for the islands. A naval operator came from
Sydney Navy Yard to take over Fanning and I
proceeded to Washington. The grief and struggle
of construction is another tale.
A manager, bookkeeper, doctor, surveyor, two
half-caste overseers, myself, and about two-
hundred natives set about building a settlement
and at the same time gathering copra. The
replacing of thatched huts by modern cottages
occupied many months of labor. Every Sunday
morning at about eleven o'clock, the Staff
assembled and in a very dignified manner made
an inspection of all work and of the native
quarters. To the manager this was a serious affair
executed with military severity, but to the others
it was a joke, and much playing took place
behind his back. A match on the floor or under
a native's house was sufficient to have the offen-
der arrested and brought before "Court" Sunday
evening. Many amusing situations developed
in "Court" and often the stern manager-judge
"lost face". There was the case of Kabuta who
refused to clean his house unless he was paid
overtime for so doing. He contended that, as the
house belonged to "The Company" he should be
paid for keeping it clean. This brought about an
impasse, and he was arbitrarily ordered to polish
it up if he expected to live in it. The following
morning native police reported Kabuta had not
slept in his house and was absent from camp.
This violated two more rules. Kabuta stated he
had spent the night sleeping on boxes of dyna-
mite in a lean-to, about a mile up the beach,
where cleaning wasn't necessary.
DISCOVERING THE AUDION
C\>-> THE morning of September 16, 1917, I
^-^ experienced the same sensation as the man
who saw the giraffe for the first time and ex-
claimed, "There isn't any such animal!" The
usual inspection was in progress, and the average
number of arrests being made, when my atten-
tion was attracted to a little glass ball suspended
from the rafters in a native's room. Wrinkling
my nose in native fashion point, I asked of the
fellow squatting on the floor, "Terrah?" He
shrugged his shoulders up around his ears and
with a puzzled expression on his chocolate fea-
tures replied, "Ungcome!" 1 extended my hand
for the thing and he passed it to me. Imagine
my astonishment to find that it was a DeForest
Audion, the first I had ever seen, but recognized
from pictures. I wanted to know where the
native had found it and he said, "Ay naka may
en tardy," (" It came here from the sea,") He had
picked it up while walking along the beach and
thought it a pretty bauble.
There is a native custom which forces one to
give up an object if the other party desiring
it merely begs for it saying, "Now! Ye pacheco."
In this manner I became the owner of the tube,
one of the strangest and most fragile bits ever
cast ashore by the pounding seas.
Remember that this was in 1917 and 1 doubt if
there was a handful of these tubes in the entire
territory contiguous to the Pacific Ocean. Some
tubular shaped Audiotrons, made in Berkeley,
California, were being used. I had a dozen myself.
The question as to where this Audion could
have come from was a difficult one to answer.
Teraina was 900 miles from the Australian sea-
lanes and 1800 miles from the courses to Tahiti
Honolulu was the nearest port and that was a
(continue*.! on fmge ;;6')
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THE HAVEN OF A SEA-GOING
AUDION
(continued from page 7/7)
thousand miles to the north'ard. Allowing a drift
of but a few miles a day, many months must
have passed and miles unwound from the point
of departure until riding the surf, this tiny glass
bulb found rest on the sands at Teraina. Study
of other drift material offered the only oppor-
tunity for conjecture.
Cocoanuts are supposed to have come from
Central America and vegetated throughout the
South Pacific. While digging an irrigation canal
on Washington Island, an old Manahikian canoe
was found. It was quite a distance inland from
the present shore of the lake and buried in gravel,
which undoubtedly was the old lagoon beach,
before the present lake was formed by the la-
goon's closing. The bow is in good condition and
now occupies a prominent position in the Bishop
Museum, Honolulu. There are legends told by
the old men of Manahiki, about travels to Te-
raina in great canoes. One tale recites how the
King of Manahiki, angered at some of his people
who refused to return from Teraina, cursed them
and cried for a tidal wave to wipe out the rebel
village. The canoe is pointed out as evidence of
Manahikian occupation and the closed lagoon as
the fulfillment of the curse.
Of more recent date is a load of lumber con-
signed to A. P. McDonald, Tahiti. This must
have been washed overboard from some schooner
and found its way to Fanning and Washington.
Fanning is 75 miles to the southeast of Washing-
ton. The lighter pieces came ashore at Washing-
ton while all the great, heavy beams piled up on
Fanning, without exception. The British Com-
missioner at Fanning seized the lumber for his
new house, quoting a law some hundreds of years
old, which claims everything from the sea for the
Crown.
Standard Oil Barge No. 95 almost foundered
off the coast of lower California. Everything on
deck was swept away. A year and a half later,
one of her steel lifeboats, buoyed by the airtight
compartments in bow and stern, majestically
floated past our island. An object resembling a
human head was visible, silhouetted against the
bright noon-day sky. Dave Greig, the overseer,
and I were the. only ones at the settlement, ex-
cept the cooks and store boys. Greig launched
a small fishing boat and started to run down the
visitor. What suspense as I stood on the beach
and watched him overtake the lifeboat! Then he
gave me the prearranged signal that there wasn't
any one aboard. After quite a struggle against
the strong current, Grieg succeeded in bringing
the boat ashore. We were surprised to find it
nearly full of water and with a great many fish
of all sizes swimming about. The bottom was
filled with fish bones, who had perhaps served as
food for later comers. Many of the bones were
from large sharks. This craft must have come
at least 5000 miles, and as it is highly improbable
that it traveled anything like a straight course,
the distance must have been many times that.
All of this drift has been from the eastward and
in each case, except the audion, a point of origin
is known. It is possible that the DeForest wan-
derer started somewhere in the Atlantic, bobbed
through the Canal, crossed the Pacific, and came
to rest, at last, on the beach at Teraina. This is
not any more difficult to believe, than the mere
fact that it came out of the sea, over a rocky reef,
to the beach — a beach whose entire length is but
eleven miles, situated in mid-Pacific where dis-
tances are measured in thousands of miles!
The cocoanuts, the canoe, the lumber, the life-
boat, and the DeForest Audion — symbols of an
age, and slender threads from other worlds —
to peaceful, detached Teraina!
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WESTON
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INSTRUMENTS
A New and Better
SHORT WAVE RECEIVER
The Aero International Four
(Rear Panel
View)
NOTICE
We can furnish
all parts for this
new receiver, in-
cluding founda-
tion unit, direct
from factory.
Write for infor-
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then plan to build this superlative
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THE new Aero "International Four" Receiver marks a distinct milestone in
radio progress.
For the first time, radio frequency amplification on short waves has become a
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in the design of this receiver.
Newly designed parts have been incorporated throughout. The tuning condenser has
no mctal-on-metal bearing, so that the hissing noises formed by the variation in contact
has been eliminated. New coils of a smaller diameter, having a much smaller external
field, a better shape factor and improved efficiency are employed. The foundation
unit with holes drilled for mounting every part, simplifies the construction of the set,
and assures proper placement of the parts. The isolation of the antenna from the
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variations in antenna lengths have little effect on the operation of the set.
The Aero "International Four" is to our knowledge the first short wave receiver of
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though due to its ease of control and great sensitivity, it is superior to most all perfect
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Uses The Aero Coil L. W. T. 10 Kit
The new kit of coils illustrated above is the L. W. T. 10, price $10.50. This kit is
designed to go with special drilled and engraved foundation unit, in which mounting
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The New Aero L. W. T. 12 Coils
This is the new Aero L. W. T. 12 kit.
Consists of 3 new small diameter Aero
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with primary coil. A pronounced im-
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All Parts Can Be Purchased Direct
We have made arrangements to supply a complete kit of all parts of the Aero Inter-
national Four direct from our factory. Write us today for descriptive literature, list
of parts, and special price list. You'll want to build and own this dandy receiver.
Send for complete information at once!
AERO PRODUCTS, Inc.
Dept. 109 1772 Wilson Ave. Chicago, 111.
Published monthly. Vol. XIII. Nn. :;. Published at Garden Cii> N.
Garden City. N. Y., as sccuiul class mail mutter. Douhioda.v. Uoran &
Subscription price 14.00 a year. Entered at the post office at
ni'aiiv. Inc.. Garden City, N V
RADIO BROADCAST
JULY, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XIII. No. 3
Cover Design - - From a Design by Harvey Hopkins Dunn
Frontispiece A Giant Radio' Equipped British Passenger Airplane 124
What Hope for Real Television? R. P. Clarion 125
The March of Radio * An Editorial Interpretation 129
Aviation Must Come to the Use of Radio
No Innovations or Revolutions for 1928
Broadcast Regulation at a Standstill
The Inequalities of "Equalization"
Another Non-Radio Man for the Commission
The Commission Eliminates Its First Station
The Engineers' Plan of Allocation
The High -Frequency Spectrum
Recent Radio Events
A New Principle in Audio Transformer Design Kendall Clough
"Radio Broadcast's" Home Study Sheets - -
No. i. The Nature of Radio and Electricity
No. 2. Determining the Capacity and Induct-
ance of a Radio Circuit
Making an A-Power Unit From Your Battery Charger
Robert Burnhatn
New Apparatus »'*-*- Useful Information on J\[ew Products
A Good Amplifier-Power Unit for the 250 Tube Howard Barclay
"Strays" from the Laboratory Keith Henney
New Crystal Control
Prices of British "Components"
Present Interesting Trends in Radio
Radio Gossip
Publications Worthy of Note
"Skim Milk Masquerades as Cream"
133
135
137
139
141
143
Technical Smoke Screen
Recent Interesting Technical Articles
Present Compression Type Resistors
From a Lab Circuit Fan
Who Our Readers Are
A Flux for Nichrome Wire
An Interesting A-B-C Power Unit and One-Stage Amplifier
/. George Uzmann
A Universal Set and Tube Tester •'*'-.'• D. A. R. Messenger
Broadcast Station Calls with a Past - • William Fenwic\
"Our Readers Suggest"
Checking Power Unit Voltages
A Convenient Telephone Jack Arrangement
Neutralizing the Short- Wave Amplifier
Wave Trap Tuned Antenna Combination
Additional Amplification for Phonograph
Pick-Up
To Stop That Whistling
As the Broadcaster Sees It •
Note on Programs
D«ign and Operation of Broadcast Stations
21. Water-Cooled Vacuum Tubes
A Space-Charge Amplifier and B Supply
A Fine Program You Will Never Hear
H. P. Manly
John Wallace
The Listener's Point of View
A Receiver for Short- Wave Broadcast Reception Bert E. Smith
Manufacturers' Booklets * -
"Radio Broadcast's" Laboratory Information Sheets - -
No. 201. Tube Life
No. aoa. Farm Lighting Systems
No. 103. Tuned Circuits
No. 204. Line Voltage Variations
No. 205. Electrical Measuring Instruments
No. 206. A Screen-Grid Resistance-Coupled
Amplifier
No. 207. Equalizing Wire Lines for Broad-
casting
No. 208. Power Values in Radio Receiving
Antennas
Letters from Readers
145
148
150
151
A Short'Wave Adapter for the R.B. Lab Receiver Hugh S. Knowles 153
How to Build a Beat'Frequency Oscillator - G. F. Lampkin 156
"Radio Broadcast's" Service Data Sheets on Manufactured
Receivers 159
No. 3. The Grebe A.C. Six No. 4. The Kolster 6 K A. C.
Carl Dreher 161
163
165
167
170
174
179
OTHER THINGS.
The contents of this magazine is indexed in The Readers* Guide
to Periodical Literature, which is on file at all public libraries.
MANY favorable comments have been received about the
list of stations throughout the world transmitting below
loo meters which occupied three pages of our May, 1928, issue.
Although this list was very carefully checked for accuracy
against the best lists of stations we could find, some errors
undoubtedly crept in. Some of our readers have been kind
enough to send us information which should be included when
the list is published again in RADIO BROADCAST. In the course of
the next four or five months we shall reprint the list, com-
pletely revised. We urge our readers to help us by sending in
any corrections which should be included at that time.
IN THIS issue we begin a new feature, "RADIO BROADCAST'S
Home Study Sheets" prepared by Keith Henney, director
of the Laboratory. Back in September, 1925, Mr. Henney's
first article, "New Fields for the Home Experimenter" under-
took to lead the radio experimenter who had tired of merely
building radio sets and who desired to learn more about what
makes the wheels go 'round. Since that time, many articles of a
similar nature have been published in these pages. With this
issue we begin the "Home Study Sheets," which are arranged
so that the interested readers can remove them with a razor
blade and keep a complete file. The Sheets to follow will contain
a great deal of practical information in what we believe is the
most useful form. We shall be glad to have our readers' opinions
on the innovation. It is a policy of RADIO BROADCAST to print
as much useful information as possible with due thought to the
form in which it is presented. The "Lab Sheets" — the 2o8th
appears in this issue — were the first in this series. Next follow
the "Service Data Sheets on Manfactured Receivers" and we
have now added the "Home Study Sheets." Still other ser-
vices, similarly valuable, are in prospect.
UNLESS we are greatly mistaken, several of the articles in
this issue are going to excite a great deal of interest. The
leading article by R. P. Clarkson, "What Hope for Real Tele-
vision7" attempts to explain television systems in general and
to point out what now seems to be the only possibility of suc-
cess.
OUR August issue will contain, among other things, a
description of the d.c. operated "Lab" circuit, another
timely article on television, a really fine article by David Grimes
on phonograph pick-up units, a constructional and operation
article on the Cooley Rayfoto system, first introduced to our
readers in our September, 1927, issue, a story on a new short-
wave receiver, and the first article of a series by Robert S. Kruse.
Mr. Kruse for a number of years was technical editor of S^ST.
His first article deals with the mystery of 5-meter work and
will be of especial interest to all our amateur friends who read
RADIO BROADCAST. All the regular features will appear in our
August issue as well.
AS THIS issue goes to press, a correction has been noted
in the list of parts (p. 142) for the article "A Good
Amplifier-Power Unit for the 250 Tube" The Dongan Con-
denser Unit, Ci, is listed at $16.50, instead of $23.00, as
printed in the list.
— WILLIS KINGSLEY WING.
OOUBLEDAT, DORAN & COMPACT, INC., Garden Qity, J^ew
MAGAZINES
COUNTRY LIFE
WORLD'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
SHORT STORIES
EDUCATIONAL REVIEW
LE PETIT JOURNAL
EL Eco
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OFFICERS
F. N. DOUBLEDAY, Chairman of the Board
NELSON DOUBLEDAY, President
GEORGE H. DORAN, rice-President
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RUSSELL DOUBLEDAY, Secretary
JOHN J. HESSIAN, Treasurer
LILLIAN A. COMSTOCK, Asst't Secretary
TORONTO: DOUBLEDAY, DORAN & GUNDY, LTD. L. J. McNAUGHTON, Asst't Treasurer
Copyright, 1928, in the United States. Newfoundland, Great Britain, Canada, and other countries by Doubleday. Doran & Company, Inc. All right* r«en*d,
TERMS: $4.00 a year; single copies J5 cents.
122
RADIO BROADCAST ADVERTISER
12.'}
Lmazing results now obtained by experimenters with
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Secondary and tickler are space-wound on a film of
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LOW-WAVE
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20, 40 and 80 Meter Bands
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80 Meter Coils 2.00 "
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A Giant British Radio- Equipped Passenger Airplane
THIS is a close-up of one of the giant DcHavilland 66
Hercules multiple-engined airships, fitted with three
Bristol Jupiter 450-horsepower engines, built for the British
Imperial Airways for the new passenger air route between
England and India via Egypt, Palestine, Mesopotamia, and
Persia. The radio cabin is the most spacious yet fitted in any
airship and contains the best apparatus now available.
Under the new international aerial regulations, a radio oper-
ator and mechanic is carried to attend to the apparatus and
operate it. Previously the radio equipment was carried in
the cockpit and operated by the pilot. The power of the
transmitter is 150 watts. The set is slung on elastic bands
to reduce vibration; the wind-driven generator, minus its
propellor, is visible just under the top wing
124
BEFORE THE BAIRD "TELEVISOR"
In spite of the miles of type expended on television it is not yet possible by
system to receive ,mages which have much detail. All the systems known are
Simitar. Although it ,s possible /or expenmenters to construct s.mple rece.vers to p«rl( up
television signals, "u-henT as, and if transmuted, the results are d.tfcult to ach,eve. The
.Ilustrarion shou* Mrs. Howe, said to be the first woman whose features were televised
across the Atlantic by the Baird system
Television?
THE promise of television is that we may
see events as they occur, no matter where
we are, provided we have a television re-
ceiver and provided, also, that a televisor opera-
tor is present at the event. Televising is the
broadcasting of images, the annihilation of dis-
tance for the eye as aural radio has done for the
ear. In place of the microphone we want to use
the camera lens together with some device that
translates light reflected from the object, into
electric current impulses which speed to our
receiver where those impulses are translated back
into light and are projected on a screen
This is the promise It seems so simple. Yet
long before regular braadcasting of programs
commenced, we were as far ahead in method as
we are now. It violates no confidence to say that
only within the last month one of the most prom-
inent workers has abandoned the problem in
favor of research on the facsimile transmission
of telegrams. Another, C. Francis Jenkins, writes
that it is a stubborn problem but the solution
seems to be right around the corner. In England,
Sir Oliver Lodge raises a note of warning against
the public expecting success, stating that other
scientists are in accord with him. Theodor
By R. P. CLARKSON
Author of "The Hysterical Background of Radio"
m
EIGHTEEN LINES TO THE INCH
This drawing shows what slight modula-
ation is required to portray the features.
The image received in some television
outfits is no larger than the actual size
of the cut above. The reader may imag-
ine the detail of the received picture
where the image of an entire head, for
example, must be included in this space
'25
Nakken, whose researches have made the photo-
electric tube available for this work, states flatly
that the thing is impossible with the methods
now being tried, except at enormous costs. With
this weight of authority against success, let us
look for a moment at the problem.
The eye is a camera, but a very defective one.
It retains an impression for a definite period,
normally about one-tenth of a second, and be-
cause of this, moving pictures are possible. On
the other hand, an impression must affect the
eye for a certain definite minimum of time, de-
pending upon the intensity of light, or it won't
register in the consciousness at all. This makes
possible the magician's tricks in dim light, and
makes almost impossible the achievement of
television.
To see any image dot by dot, the first essential
is that the eye must see each dot for a period
long enough to awake the consciousness, and yet
it must see the last dot of the image before the
impress:on of the first dot is lost. To put this in
figures means that the last dot must be shown
within a tenth of a second after the first dot, and
yet each dot must appear for at least the five-
hundred-thousandth part of a second, strongly
126
RADIO BROADCAST
JULY, 1928
BAIRD'S FIRST "TELEVISOR"
This crude but workable apparatus, undoubtedly the result of much labor on the part of Baird, who,
like most inventors dependent upon their own resources, had very little money with which to carry
on his experiments, gives an idea of how simple is the essential apparatus required for the production
of television signals. The various disks function to break up the object to be transmitted into many
tiny dots so that the light finally reaching the photoelectric cell is broken up into many consecutive
impulses each of which corresponds in intensity to one particular spot of the subject. This original
model has been placed on view at the Science Museum, at South Kensington, London
illuminated. These two figures determine the size
and quality of the possible image. They indicate
50,000 dots to the picture as substantially the
possible maximum and strong artificial illumina-
tion as essential at the receiver, unless some way
is found to maintain the illumination of the dots
beyond the period of their stimulus.
Transmitting an image and transmitting a
musical composition are accomplished in the
same way. The music is sent note by note in
ordered sequence. We enjoy it as it is produced.
A picture is similarly subdivided into dots of
light and shade and these dots sent in any se-
quence, but they must all be received and placed
in proper relationship before there is any picture.
There is nothing to see until the transmission is
ended. In telephotography, time is no bar to
transmission because each dot is permanently
recorded as received, and when transmission is
ended we have a complete record. In television,
each image is fleeting. There is no record. It is
all over in a tenth of a second and the next image
is on the way. Time is of the essence of television.
It is largely the problem of time that makes suc-
cessful telephotography meaningless with respect
to television. A small picture sent in five minutes
is commercially perfect but to send 3000 pictures
of the same size in the same length of time is an-
other story.
REQUIREMENTS OF A GOOD PICTURE
XTEGLECTING color and form, for the mo-
' ' ment, all pictures and images differ from
each other only in the distribution of light and
shade. The range of light intensities is of the
order of one to thirty, as we go from deepest
shadow to brightest light. But all these intensities
are not usually sharply defined. They may shade
into each other abruptly, however, as in the case
of a church steeple standing out against a white
cloud. Draw an imaginary line across the steeple
and follow in your mind the changing light and
shade along that line. From the white of the
cloud you may change suddenly to a very dark
edge of the steeple, and then come a continual
series of changes through all shades as the detail
of the steeple is recorded. Across a peaceful land-
scape even greater variations may be found as
you follow a straight line through clouds, trees.
leaves and grasses, flowers, dirt, stones, pebbles,
and whatnot. These changes in light and shade
are the "modulation" of the picture.
Long experience with half-tones has shown
that to produce a really good picture, provision
must be made to reproduce 130 to 150 changes
in light and shade to each lineal inch. This same
modulation may be required up and down a ver-
tical line as well as sideways along the horizontal.
In other words, the modulation figure for a
square inch may be of theorderof 20,000 changes.
If the figure is made up of dots, 20,000 of them
have to be printed to give the detail of a fine
half-tone. On cheap news print, where the sur-
face itself is rough, as low as 2500 dots per square
inch are used in the poorest of newspaper re-
productions. Most of the New York papers use
3969 dots per square inch, while this magazine
and other popular ones on good paper uniformly
use 14,400 dots to the square inch. Even with
the highest of all these figures, however, details
of cloud effects cannot be reproduced and the
beautiful lights and shadows of woodcuts are
impossible.
In our television screen image let us aim no
higher than the detail of a news print photograph.
For each square inch of the picture there must be
2500 dots transmitted. For an image one foot
square, which wouldn't give much of a view of a
spectacle such as a ball game, there would be
360,000 dots. The last dot must arrive within a
tenth of a second after the first dot, so the rate
of transmission over a single waveband would be
3,600,000 dots or impulses per second. Each dot
would exist only that small fraction of a second
/Television signals from
V Radio Receiver.
Light
Neon Tube lighted
with signals from
Receiver
Revolving
Lens Disc"
Output to Transmitter
Antenna system
Image produced by
light from Neon Tube
\
Slot in
Disc"
Image on Translucent
Screen
Lenses
BAIRD S TELEVISION RECEIVER
This shows the arrangement of the revolving disc, neon tube and trans-
lucent screen used in one model of the Baird television receiver. The
light from the neon tube, varying in accordance with the picture signals,
passes through the lenses in the revolving disc (which must rotate in
synchrony with the transmitting apparatus) which focus the light on the
screen; the image is viewed from the opposite side of the screen. The
general system used here is very similar to that used by Dr. E. F. W.
Alexanderson of the General F^lectric Company in his recent demonstra-
tion at Schenectady. The only difference was that the lenses in the disc
and the screen were dispensed with and the observer saw the image by
looking at the neon tube directly through the revolving disc. The received
image is red in color — a characteristic of all television reception using
neon tubes, with their characteristic red glow
Shortwave/
Transmitter
Subject
THE BAIRD TELEVISOR
This transmitter, the result of experiments by J. L. Baird, makes use of
infra-red rays, invisible to the human eye, but capable of affecting the
photoelectric cell which converts the varying light signals into corre-
sponding electric impulses. The infra-red rays, reflected from the subject
transmitted, pass through the cellular structure which breaks up the
light into many small sections or dots. The light then passes through the
two revolving discs which rotate in such a manner as to expose to the
light-sensitive cell at any moment only one of the light beams from the
cellular structure. The resulting electric impulses are then caused to
modulate the radio transmitter. The use of infra-red rays is not essential
to the operation of this camera. Electrically, the system will function
satisfactorily with any type of rays to which the photoelectric cell will
respond. The amount of illumination required is quite intense, however,
and, if ordinary lights were used, one would not be able lo endure the
intense glare for very long
JULY, 1928
WHAT HOPE FOR REAL TELEVISION?
127
and would obviously never register on the eye
unless it happened to be repeated in successive
pictures, and possibly not then. It would be so
repeated, of course, unless motion had ensued in
the intervening tenth of a second If there had
been motion that part of the picture would be
blank. This is the first difference we find between
motion pictures and television. In the movies we
see a blow start and see the arrival of the fist.
We imagine the rest of it just as we see the suc-
cessive positions of a speeding automobile and
imagine the continuity. Only by speeding up the
camera to get intervening snaps and presenting
them in slow motion do we get detail. Bach com-
plete picture flashes at once. In television, be-
cause of subdivision into dots, only one dot is
shown at a time and the mind will not retain
this short flash during the remainder of the pic-
ture. We must make the screen retain the dot
for us.
A second distinction comes from the fact that
we cannot enlarge the picture received in tele-
vision with any increased detail in the result.
We have chosen the minimum number of dots
per square inch to give a passable image. If this
is enlarged by a projecting lens, we simply sepa-
48 times each second, arm energizes
50 segments across one ro*,2500
segments excited 18 times each second
gives 45.000 light images per second
AnooV Ctthode
'-Lei*
'-Wire to Grid of
Transmitting Amplifier
CAMERA CATHODE RAY OSCILLOGRAPH
THE SWINTON-CLARKSON TELEVISION
CAMERA
I n this device the person or object to be televised
is located in front of the lens, the lens func-
tioning to focus the reflected light from the ob-
ject onto the plate. A stream of electrons from
the cathode is attracted to the positively
charged anode and a great many of the electrons
pass through the hole in the anode plate and
reach a group of photoelectric cells. In passing
through the space between the hole in the anode
and the plate the electrons come under the
influence of the two coils A and B; coil A causing
the stream to be deflected up and down the
plate and coil B causing the stream to move
back and forth across the cells. The image on
the plate is scanned in this manner
rate the dots. If we magnify the size ten times
we'll have only 250 dots per square inch and only
at a distance will this give the effect of a photo-
graph. We haven't even the value of a printed
half-tone where the dots are of varying size and
shape as well as shade. Our dots are uniform ex-
cept in shade. This may be overcome by the
screen in the device described later.
Now, getting back to the 3,600,000 impulses
per second. This is equivalent to the modulation
frequency in aural radio. The minimum fre-
quency of the carrier would be about ten times
that, or a frequency of 36,000 kilocycles, approx-
imately eight meters. A larger picture or a better
picture would drive us down to still shorter
waves.
A FOUR-INCH SQUARE IMAGE
CUPPOSE, instead of a foot square, we make
*^ the image four inches square. Even this
would mean 40,000 dots for each picture or
400.000 impulses per second. Our carrier max-
imum would be 75 meters. Even suppressing one
side band, the 400,000 modulation frequency
Incoming "Image" signals
from Photo -Electric cells
at sender
calls for a receiver to
amplify evenly over a
band of 400 kilocycles
or as much as 40 of our
present broadcast chan-
nels. This is for a tiny
picture of poor quality
and minimum speed. For
any fast event, for a
larger picture, or for
even newspaper quality,
what a complex receiver
must be devised! One
such station would blan-
ket the entire broadcast
spectrum.
Go down in size and
quality, if you will. A
three-inch square pic-
ture with 2 5 modulations
to the lineal inch or 625
dots to the square inch,
means only 56,250 im-
pulses per second. The
carrier could be as high
as 535 meters but our
tuning and amplifica-
tion would be over five
channels 10,000 cycles wide. To get within the
legal separation of stations we can use a modula-
tion of only 5000 impulses per second which, for
a barely recognizable image, would give us only
one square inch, remembering that we must send
10 pictures a second.
What, then, is Baird in England doing, for
example? Obviously the only thing he can do
and basically the only thing that has ever been
done in television. That is, to select as the object
to be televised, something that has few grada-
tions of light and shade and extremely slow
movement. This is the human face. It is a fami-
liar object, almost entirely white space with the
shadows around eyes and nose very ill defined
and their outline of no particular importance in
recognition. The cartoonists have taught us that
we need nodetail of afaceto recognizethe person.
There is always some outstanding characteristic
that suffices. Slight blurring would rather soften
the result instead of spoiling it.
Television is not achieved merely because see-
ing faces at a distance has been and will be ac-
complished. It was in recognition of this fact that
the English publication Popular Wireless un-
successfully sought to induce Baird to televise
a simple cube in slow motion to win the sum of
§5000 that magazine offered. That Baird ignored
the challenge must merely mean that he, too,
recognizes the limitations of his apparatus.
There are other problems besides that of time
in its relation to the defects of vision. There is
the question of synchronizing the mechanically
moving parts of transmitter and receiver. When
things happen in the hundred-thousandth part
of a second, there is need for absolute accord on
both ends of the line. If the same power line is
available at both ends, synchronous motors may
be kept in step, but this exists only in few local-
ities and over short distances. Synchronizing by
this means it is not a real solution of the problem.
THE REAL DIFFICULTY
AS THIS brief review indicates, the real draw-
back is the fact that the picture must be
subdivided and sent as a sequence of impulses.
We would face similar difficulties with sound
broadcasting if, for example, we had to send the
whole of an opera selection as one blare of noise
in 3 tenth of a second. It could be done, of course,
by securing a sufficient number of musicians so
that each need sound but one note. Then, at a
given signal, every musician in this enormous
Neon Gas-.
Potential sufficient to
cause Neon Gas to glow
THE BELL TELEPHONE LABORATORIES
TELEVISION RECEIVER
A large neon tube forms the basis of this television receiver. On the back
side of the tube 2500 segments of tin foil are cemented, connecting by
means of individual wires to 2500 segments on the commutator, which
revolves in synchrony with the apparatus at the transmitter. The incom-
ing signals, modulated in accordance with the shading of the subject being
transmitted, are amplified and cause segments of the neon tube to glow
with a brilliancy dependent upon the shading of the subject being
transmitted
orchestra would sound his note and go home. We
would receive the opera selection but it would
hardly be worth while. Yet this is exactly what
the eye demands in television.
One thought has been to divide the object into
units. That is, in terms of pictures, not to send
the whole picture over one carrier but, in effect,
send, say, 144 pictures, each an inch square, and
at the receiver these would make up into a single
image one foot square. This was one of the first
ideas suggested as long ago as 1880. Carried to
its extreme, perfect results would be achieved
but, within the limits of costs and apparatus, we
merely multiply our troubles. Sixteen pictures
3 inches square might be managed if we could
send anything but a crude 3-inch-square picture.
It would be at 16 times the cost and 16 trans-
mitters as well as 16 receivers would be needed
and all would have to be synchronized. Along
similar lines was Doctor Alexanderson's bundle
Coil A
Perforated Stop Plan
:with fixed opening
-B
Defecting
Plate
Wire from , -
Receiver Amplifier
CAMPBELL SWINTON TELEVISION
PROJ ECTOR
This television projector, sometimes called a
television receiver, uses an arrangement similar
to that incorporated in the Campbell Swinton
camera suggested in 1908. The electron stream
from the cathode is caused to scan the fluorescent
screen due to the action of the coils A and B,
their intensity being varied by means of the two
deflecting plates. Potential from the receiver am-
plifier is impressed on the deflecting plates and
causes the number of electrons passing through
the opening in the stop plate to vary in accord-
ance with the image signals from the transmitter.
The screen at the left of the camera becomes
fluorescent under theaction of the electron stream
and the image then becomes visible to any one
standing in front of the screen
128
RADIO BROADCAST
JULY, 1928
CAMERA
P and Fare the
elements of a special
two electrode
Vacuum Tube
THE CLARKSON TELEVISION PROJECTOR
This projector makes use of a three-electrode tube, the grid of
which functions to control the electron stream from the filament
F. The electrons passing through the opening in the plate P are
caused to scan the screen due to the action of the two coils A
and B. A phosphorescent screen (rather than a fluorescent screen)
is used so that the screen will continue to glow for an interval
after the impulse stimulus' is removed. This results in consider-
able improvement for it reduces the amount of light required
and also permits the use of a greater number of impulses so that
greater detail may be obtained
of seven light rays analyzing the object, instead
of one, and Doctor Ives' experiment with sub-
divided photoelectric cell and screen.
The Englishman, A. A. Campbell Swinton, in
a letter to Nature, June 18, 1908, and more in de-
tail in his Presidential Address to the Rontgen
Society, November 7, 1911, set forth the genesis
of an idea along these lines but one never given
publicity and never tried out. I have taken the
liberty of modifying this idea and present it
herewith as a last desperate hope.
IS THIS THE WAY OUT?
IN ALL other television devices before the pub-
' lie at present the method of telephotography
is being used, speeded up to the tenth-second
requirement. At the transmitter is a photoelectric
cell. A beam of light explores the object to be
"televised" and is reflected to the cell. This cell
modulates the carrier wave, just as though it
were a microphone. Varying light actuates it
just as varying sound actuates the microphone.
At the receiver, in place of the loud speaker, is a
glow lamp — usually a neon tube in one form or
another — which changes its brilliancy in step
with the received impulses from the photoelec-
tric cell. The light from this lamp is made to
explore a screen in synchronism with the beam
at the transmitter. The usual method of swinging
the beams of light up and down and over the
object and screen, is a mechanically revolving
disc perforated spirally with holes, a device pa-
tented by Nipkow in 1884, this inventor being
the first to see the advantage of breaking up a
picture into lines.
In the Swinton method there
is no mechanically moving part.
The object is illuminated
strongly and we have a "televis-
ion camera," let us say, which
projects the image to be trans-
mitted, not on a film, but on a
composite plate made of tiny
cubes of photoelectric material
insulated from each other. The
camera is gas tight and filled with
sodium vapor, which conducts
negative electrons more readily
under the influence of light. Be-
tween the projecting lens and
the composite plate, in the
vapor chamber, is a gauze wire
screen. The charge on this gauze
screen modulates the transmit-
ting tube.
In effect, the gauze screen
is connected by radio to a plate
in the receiver projection appa-
ratus. A beam of cathode rays is
directed past this plate towards
a sensitive fluorescent screen.
Only when the rays are slightly
bent by the repulsion of the plate
can they pass through a fixed
opening and actually be directed
to the fluorescent screen to cause
a luminous spot.
At the transmitting end there
is also a cathode-ray beam continually searching
the composite plate of the camera but on the
back side from where the image illuminates it.
As this stream strikes each little photoelectric
cube, it charges it negatively but the charge is
dissipated unless that cube is illuminated on the
front by light from the object. In the latter case,
the charge of the cube will
pass away through the ionized
vapor along the illuminating
beam of light until it reaches
the gauze screen, whereupon
that charge becomes an im-
pulse carried over to the re-
ceiver projection apparatus
where it charges the deflect-
ing plate which bends the
synchronized cathode ray so
that a luminous spot is formed
on the fluorescent screen.
Each received impulse must
correspond in position to the
illuminated cube of the com-
posite plate, requiring the syn-
chronizing of the two cathode
ray beams. This may be done
at each end separately through
the same construction as the
cathode ray oscillograph, the
beam being moved by the mag-
netic field of two coils at right
angles to each other and hav-
ing widely differing frequencies
as 10 and 1000 cycles or 10 and
10,000 cycles. Substantially
the two rays are merely tracing curves of great
amplitude and rather low frequency.
In this method the object itself is not explored
but its projected image is automatically sub-
divided by the composite plate of the camera,
which has no electrical connections. Only one
carrier wave is required but we still have the
broad band of frequencies to detect and amplify
at the receiver. No mechanically moving parts
are used. A telephoto lens, a wide angle lens or
any usual camera arrangement may be used at
will. Synchronizing presents no difficulties and
the method is as adaptable to wire as to radio.
But as yet it has not been found practical, the
main reason being that the use of photoelectric
material in the composite plate means that elec-
trons will be given off continually as long as light
falls on the plate, and in mass when the image
shifts.
In the writer's proposed modification of the
Swinton device, the material of the composite
plate is non-photoelectric but conductive. The
writer uses a closed electric circuit of which the
exploring electron beam is a part, the conductive
cube is a part when the beam strikes it. and the
ionized path in the vapor is the varying part of
the circuit. An amplifying tube is readily coupled
to this circuit.
In the projector proposed by the writer, he
suggests the use of a three-electrode vacuum
tube, using a heavily biased grid, the incoming
signal modulating that grid, as usual, and per-
mitting the flow of an electron beam. The ob-
serving screen must be phosphorescent, instead
of fluorescent. That is, it must glow for a time
after the impulse strikes it.
If any method within our knowledge has possi-
bilities, this is it. If it fails, television will await
the genius who conceives some new way of break-
ing up an image. There is no other hope.
L
P,G and F are the elements
of a special Vacuum Tube
THE CLARKSON TELEVISION CAMERA
In this arrangement a closed electric circuit exists from the source
of electrons F through the beam of electrons, which act as a
flexible conductor, to any conductive member of the non-
photoelectric composite plate, through the plate to the wire
gauze screen, along the screen to the coupling resistance and
back to the filament circuit. The object to be televised stands
in front of the lens at the left
IMh.W.N AND IIMimPKMAHQN OK IlKKHVI KAniQ KVUM 1 N
Aviation Must Come to the Use of Radio
THE question of wireless received serious
consideration," wrote Commandant James
C. Fitzmaurice in the New York Times,
after the first westward airplane flight across
the Atlantic, "but it was decided that an ef-
ficient and useful wireless set would weigh ap-
proximately 180 pounds. It was decided that
this weight of benzol would be better. This was
the one weak point in the organization of the
flight, as we now realize that had we had a wire-
less set on board, upon our estimated arrival in
the neighborhood of Newfoundland, we could
have been given almost our exact position by
the direction-finding stations along the coast
and informed of the precise direction and veloc-
ity of the wind over the area, and we would have
made New York easily and accomplished our
objective. We consider wireless absolutely neces-
sary for all future undertakings of this nature."
If radio could have enabled the German fliers
to reach their goal, it may be argued with equal
force that Nungesser, Coli, Hinchcliffe, Hamil-
ton, St. Roman, and the other transatlantic
fliers might well have made safe landings, guided
through the hazardous Newfoundland region
by compass bearings from Cape Race, Belle Isle,
and Chebucto Head. Had the Bremen been
properly equipped with radio, she would have
landed in an airport and Floyd Bennett's tragic
flight to aid the German aviators would have
been unnecessary. Last year, the Bremen started
a westward flight across the Atlantic but,
warned by radio of unfavorable weather, re-
turned to safety. Byrd's transatlantic flight was
successful largely because of radio beacon sig-
nals although he did not make the most of his
installation. Those who attempt long-distance
flights without the aid that radio can give them,
heroes or not, are both unscientific and fool-
hardy. The fact that some succeed in their
undertaking without radio is no justification for
recklessness.
Only when transatlantic and international
flights become common and scheduled occur-
rences will long-distance flying take its place
among the useful arts of human society. Like
radio, aviation must become a regular service
which is expected to function satisfactorily and
without failure.
The scientific development of aeronautics has
already advanced to the point where we have
aircraft and aircraft motors which are entirely
serviceable and reliable. Ships can be built to
meet almost any reasonable requirement. Mo-
tors are still uneconomically shortlived, but
their limitations are so well known that an
ample factor of safety for any reasonable flight
can be provided.
The principal obstacles to everyday use of
aviation are safety and cost. When the problem
of safety is solved, the public will so quickly
accept the airplane as a means of rapid travel
that the cost of flights will fall to a point jus-
tified by the time which they save. Public con-
fidence, based on reliable service, rather than
spectacular feats, is the greatest need of avia-
tion.
The development of radio communication as
an integral part of our commercial flying struc-
ture is the most important and the most neg-
lected step to promoting safety in aviation. Its
general adoption is not so much a matter of
developing new equipment as one of convincing
the aircraft industry of the value of radio.
Radio serves the aeronaut in several distinct
capacities. At all important landing fields, radio
stations are required for the exchange of weather
reports, to report the leaving and arrival of
ships, to issue orders to aircraft in flight and to
disseminate periodic weather reports. With a
properly coordinated system of collecting and
distributing weather information, storm warn-
ings can be issued in ample time to assure the
comfort of passengers and the safety of cargo.
At least 500 low-power transmitting stations for
this purpose will ultimately be required, as well
as a few high-power transmitters to broadcast
information to these landing field stations.
Another important function of radio is to
mark out the highways of the air and to keep the
aviator on his course. The aircraft direction
beacon, which radiates two directional signals at
forty-five degrees from the prescribed course,
has demonstrated its usefulness. The radiated
signals consist of mechanically sent dots and
dashes, so timed that, when a flier is exactly on
his course, the combined signal received from
both directional stations equally forms a single
series of dashes. But should the pilot deviate
from his course, the signal from one of the direc-
tional antennas predominates and produces a
ABOARD A PRIVATE MOTOR YACHT
The motor yacht Crusader, owned by A. K'
Macomber of California is one of the most elab-
orately fitted yachts afloat, from the radio
point of view. The ship has elaborate broadcast
receiving equipment with loud speaker outlets
in nearly every cabin. The illustration shows the
o.;-kw. voice transmitter aboard the Crusader
129
distinctive signal, enabling him to determine
whether the plane is to the right or to the left
of the prescribed course. At a distance of more
than fifty miles, short-wave beacons become
erratic in their behavior and directional readings
unreliable. Therefore aircraft direction beacons
should be placed in operation each one hundred
miles along the principal highways of the air.
A third service is the aircraft beacon or radio
lighthouse which gives a distinctive signal to a
ship in flight when it is within a definite distance
of a given marker point. In foggy and heavy
weather, the radio beacon enables the flier to
come sufficiently close to the landing field that
its neon light beacon can guide him to a safe
landing. Literally thousands of these low-power
marker beacons are required to serve as the sign
posts on the highways of the air.
Recently, the Department of Commerce
awarded a contract covering radio equipment
for twelve radio-controlled stations, six radio
beacons and twelve markers, at a total cost of
slightly more than $150,000. The Assistant
Secretary of Commerce for Aeronautics, William
P. MacCracken, stated:
"Radio telephone communication to the air-
plane is expected materially to decrease acci-
dents and provide for stability of schedules
with greater comfort to air travelers and may
be considered the greatest need of air trans-
portation to-day."
The leaders of research in the radio industry
have by no means neglected the requirements of
aviation. The General Electric Company and
the Westinghouse Company have developed
standard models of directional signal transmit-
ters and beacon equipment. The American
Telephone & Telegraph Company has recently
added an airplane to its experimental equipment
at \\ hippany in order to perfect various types of
aircraft radio-communication apparatus. Re-
ceivers which give visual indication of direction
have been developed.
The principal obstacle to the use of radio on
aircraft arises out of the fact that radio is con-
sidered by the greater number of pilots only as
an additional burden and nuisance. The airmen's
opposition is singularly reminiscent of the ridi-
cule which sea captains accorded radio when
the first installations were being made on pas-
senger ships. It required more than a decade of
education to make the sailor welcome the radio
operator. The aircraft pilot remembers radio as a
necessary evil to his course in military flying.
He complains of the radio helmet which he must
wear, because it prevents him from hearing the
functioning of his motors. His ear must be ever
alert to observe the slightest irregularity in their
functioning.